Queen dowager

A queen dowager or dowager queen is a title or status generally held by the widow of a king. In the case of the widow of an emperor, the title of empress dowager is used. Its full meaning is clear from the two words from which it is composed: queen indicates someone who served as queen consort, while dowager indicates a woman who continues to hold the title from her deceased husband. A queen mother is a former queen consort, often a dowager queen, who is the mother of the reigning monarch.
there are three queens dowager: Kesang Choden of Bhutan, Norodom Monineath of Cambodia, and Lisa Najeeb Halaby of Jordan.

Status

A queen dowager has an important royal position but does not normally have any rights to succeed a king as monarch on his death unless she happens to be next in line to the throne.
A queen dowager continues to enjoy the title, style, and precedence of a queen, but is no longer referred to as the queen. A new reigning king would have a wife who would be the new queen consort and therefore the queen; a queen regnant would also be called the queen. Many former queens consort do not formally use the word "dowager" as part of their titles. There may be more than one queen dowager at any given time. The Garter King of Arms's proclamation in the United Kingdom of the styles and titles of Queen Elizabeth The Queen Mother at her funeral on 9 April 2002 illustrates her dual status as a queen dowager and a queen mother:

Distinction from queen mother

A queen mother is a former queen, often a queen dowager, who is the mother of the current monarch. Not every queen mother is a queen dowager, such as Queen Paola of Belgium, who became the queen mother of her son Philippe after her husband Albert II abdicated the throne but retained the title of king. Not all queens dowager are the queen mother; they may have a relation other than mother to the reigning monarch, such as aunt or grandmother. For example, Mary, Queen of Scots, was queen dowager of France after the death of her husband Francis II, to whom she bore no children. Similarly, Adelaide of Saxe-Meiningen was queen dowager after her husband William IV was succeeded by his niece Victoria.
Not every mother of a reigning monarch is the queen mother or a queen dowager. For example, the mother of Queen Victoria of United Kingdom, Victoria of Saxe-Coburg-Saalfeld, was neither a queen dowager nor the queen mother because her husband, Edward Augustus, Duke of Kent, had never been king. Similarly, whilst being the mothers of monarchs, both Augusta of Saxe-Gotha and Srinagarindra of Thailand were not styled queen dowager because their respective husbands, Frederick, Prince of Wales and Mahidol Adulyadej, Prince of Songkla, were never kings. Instead, Augusta held the title of "Dowager Princess of Wales" ; Srinagarindra meanwhile received the designation "Princess Mother".
As there is only one monarch, there can only be one queen mother. It is possible for there to be a queen mother and one or more queens dowager alive at any one time. This situation occurred in the Commonwealth realms in the period between the accession of Queen Elizabeth II on 6 February 1952 and the death of her paternal grandmother on 24 March 1953, when, for slightly over a year, there were three queens alive:

Queen Elizabeth II.
Queen Elizabeth The Queen Mother, the widow of the deceased King George VI and the mother of the reigning queen. Queen Elizabeth, the former queen consort, specifically adopted the appellation queen mother to distinguish herself from her daughter, Queen Elizabeth II. She reportedly loathed being referred to as a dowager queen, and felt there would be confusion if she were called simply by her name, as her two immediate predecessors, Queen Mary and Queen Alexandra, had been.
Queen Mary, the widow of King George V, the mother of the former king Edward VIII and of the late King George VI. Queen Mary had been the queen mother from the death of her husband in 1936 until the accession of her granddaughter, Queen Elizabeth II, in 1952. She continued to be titled and styled Her Majesty Queen Mary.
British queens dowager

There were several former queens consort of England, Scotland, and later the United Kingdom, who were never queen mothers. The following queens were dowagers between the given dates, whether queen mothers or not:
Of England:

Edith of Wessex 5 January 1066 – 18 December 1075, wife of Edward the Confessor; sister of Harold Godwinson.
Adeliza of Louvain 1 December 1135 – 23 April 1151, wife of Henry I of England; remarried to William d'Aubigny, 1st Earl of Arundel in 1139.
Eleanor of Aquitaine 6 July 1189 – 1 April 1204, wife of Henry II of England; queen mother to Richard I and John.
Berengaria of Navarre 6 April 1199 – 23 December 1230, wife of Richard I of England.
Isabella of Angoulême 18/19 October 1216 – 31 May 1246, wife of John of England and queen mother to Henry III of England. Remarried to Hugh X of Lusignan 1220.
Eleanor of Provence 16 November 1272 – 24 June 1291, wife of Henry III of England and queen mother to Edward I of England.
Marguerite of France 7 July 1307 – 14 February 1317, wife of Edward I of England and stepmother to Edward II of England.
Isabella of France September 1327 – 22 August 1358, wife of Edward II of England and queen mother to Edward III of England, from her husband's deposition on 20 January 1327.
Isabella of Valois 14 February 1399 – 13 September 1409, wife of Richard II of England; ceased to be queen consort with Richard's deposition on 30 September 1399. Remarried to Charles I de Valois, Duke of Orléans on 29 June 1406.
Joanna of Navarre 20 March 1413—9 July 1437, wife of Henry IV of England and stepmother to Henry V of England.
Catherine of Valois 31 August 1422 – 3 January 1437, wife of Henry V of England and queen mother to Henry VI of England. Remarried to Owen Tudor in 1428 or 1429.
Margaret of Anjou 21 May 1471 – 25 August 1482, wife of Henry VI of England.
Elizabeth Woodville 9 April 1483 – 8 June 1492, wife of Edward IV of England and queen mother to Edward V of England until the latter's deposition in 1483.

Of England and Ireland

Catherine Parr 28 January 1547 – 5 September 1548, sixth and last wife of Henry VIII of England and stepmother to his children King Edward VI, Lady Mary and Lady Elizabeth. Remarried to Thomas Seymour, 1st Baron Seymour of Sudeley most likely in mid-spring of 1547 and was mother to Mary Seymour.

Of Scotland

Margaret of Wessex 13 November 1093 – 6 November 1093, wife of Malcolm III of Scotland.
Ermengarde de Beaumont 4 December 1214 – 12 February 1233/34, wife of William I of Scotland and queen mother to Alexander II of Scotland.
Marie de Coucy 6 July 1249 – 1285, wife of Alexander II of Scotland and queen mother to Alexander III of Scotland. Remarried to Jean de Brienne in 1257.
Yolande of Dreux 19 March 1286 – 2 August 1322, wife of Alexander III of Scotland. Remarried to Arthur II, Duke of Brittany in 1292.
Joan Beaufort 21 February 1437 – 15 July 1445, wife of James I of Scotland and queen mother to James II of Scotland. Remarried to James Stewart in 1439.
Mary of Guelders 3 August 1460 – 1 December 1463, wife of James II of Scotland and queen mother to James III of Scotland.
Margaret Tudor 9 September 1513 – 8 October 1541, wife of James IV of Scotland and queen mother to James V of Scotland. Remarried to Archibald Douglas, 6th Earl of Angus in 1514 and Henry Stewart, 1st Lord Methven in 1528.
Mary of Guise 14 December 1542 – 11 June 1560, wife of James V of Scotland and queen mother to Mary, Queen of Scots.

Of England, Ireland and Scotland

Henrietta Maria of France 30 January 1649 – 10 September 1669, wife of Charles I and queen mother to Charles II.
Catherine of Braganza 6 February 1685 – 30 November 1705, wife of Charles II.
Mary of Modena 16 September 1701 – 7 May 1718, wife of James II and VII; ceased to be queen consort with his deposition on 11 December 1688.

Of the United Kingdom:

Adelaide of Saxe-Meiningen 20 June 1837 – 2 December 1849, wife of William IV.
Alexandra of Denmark 6 May 1910 – 20 November 1925, wife of Edward VII, queen mother to George V.
Mary of Teck 20 January 1936 – 24 March 1953, wife of George V, queen mother to Edward VIII and George VI until the latter's death on 6 February 1952.
Elizabeth Bowes-Lyon 6 February 1952 – 30 March 2002, wife of George VI and queen mother to Elizabeth II – styled as Queen Elizabeth The Queen Mother.

If the current queen consort, Queen Camilla, outlives the incumbent king, King Charles III, she will become a queen dowager, while King Charles’s son and daughter in law become the new king and queen consort respectively. She would not be known as a queen mother, as she is not the biological parent of Prince William.

Other

Note that in some of the countries mentioned below it is unusual to indicate a former queen-consort as a dowager.

East Asia

China

Queen Dowager Xuan, concubine of King Xiaowen and mother of King Zhaoxiang of Qin.
Queen Dowager Zhao, wife of King Zhuangxiang of Qin and mother of Qin Shi Huang.
Empress Lü, wife of Emperor Gaozu of Han.
Wu Zetian, wife of Emperor Gaozong and mother of Emperors Zhongzong and Ruizong of Tang. Later became the only Empress regnant in the history of China.
Empress Dowager Cixi, wife of Xianfeng Emperor and mother of Tongzhi Emperor of Qing.
Japan
Empress Dowager Eishō, wife and widow of Emperor Kōmei of Japan.
Empress Shōken, wife and widow of Emperor Meiji of Japan.
Empress Teimei, wife and widow of Emperor Taishō of Japan and mother of Emperor Shōwa.
Empress Kōjun, wife and widow of Emperor Shōwa of Japan and mother of Emperor Akihito.