Homily

A homily is a commentary that follows a reading of scripture, giving the "public explanation of a sacred doctrine" or text. The works of Origen and John Chrysostom are considered exemplary forms of Christian homily.
In Catholic, Anglican, Lutheran, and Eastern Orthodox churches, a homily is usually given during Mass at the end of the Liturgy of the Word. Many people consider it synonymous with a sermon.
The English word homily is derived from the Ancient Greek word ὁμιλία homilia, which means intercourse or interaction with other people. The word is used in . The related verb is used in, and in, both used in the sense of "speaking with". The word later came to have a more technical sense. According to The Catholic Encyclopedia, Origen was the first to distinguish between logos and homilia.

Roman Catholic Mass homily

The General Instruction of the Roman Missal, the official document governing the celebration of Catholic Church|Mass], states that:
The GIRM and the 1983 Code of Canon Law prescribe that the preaching of the Homily is reserved to ordained ministers and never to lay persons, and is required on Sundays, Holy Days of Obligation, and Masses that are celebrated with the participation of a congregation.

Other senses

Contemporary Protestant clergy often use the term 'homily' to describe a short sermon, such as one created for a wedding or funeral.
In colloquial, non-religious, usage, homily often means a sermon concerning a practical matter, a moralizing lecture or admonition, or an inspirational saying or platitude, but sermon is the more appropriate word in these cases.