Ekaggata

Ekaggatā is a Pali Buddhist term, meaning tranquility of mind or one-pointedness, but also "unification of mind."
According to the Theravada-tradition, in their reinterpretation of jhana as one-pointed concentration, this mental factor is the primary component in all jhānas and the essence of concentration or samādhi. One-pointedness temporarily inhibits sensual desire, a necessary condition for any meditative attainment. Ekaggatā exercises the function of closely contemplating the object, the salient characteristic of jhāna, but it cannot perform this function alone. It requires the joint action of the other four jhāna factors each performing its own special function: vitakka, vicāra, pīti, and sukha.
Ekaggatā is identified within the Buddhist teachings as:

One of the seven universal mental factors within the Theravada abhidharma teachings.
One of the qualities associated with the second jhāna, according to the Pali Canon.
Antidote to sensory desire within the five hindrances.

Etymology

Ekaggatā means:

"one-pointedness", or the state of having one point ;
"unification of mind," in which mind becomes very still but does not merge with the object of attention.

Definition

Theravada monk Bhikkhu Bodhi states:
Bhikkhu Bodhi also notes that deeper, more profound concentration concentration causes peace. This is thought to arise from and is founded in happiness.
Nina van Gorkom explains:
The Atthasālinī elaborates ekaggatā :
Ajahn Sucitto further explains:
Yet, Richard Shankman notes that ekaggata also means "unification of mind," in which mind becomes very still but does not merge with the object of attention, and is thus able to observe and gain insight into the changing flow of experience.