Definitions

1. noun

plural of focus: a point of concentration or convergence; especially, in mathematics, the point inside an ellipse or hyperbola at which the sum of the distances to two fixed points (the foci) is constant.

“The camera’s foci were carefully adjusted to ensure a sharp image.”

2. verb

to focus or concentrate (something) at a particular point or place

“The sun’s rays foci on a single spot, causing a burning sensation.”