Yes, foci is a Scrabble word!

Noun

1. The concentration of attention or energy on something

2. Maximum clarity or distinctness of an image rendered by an optical system

3. Maximum clarity or distinctness of an idea

4. A central point or locus of an infection in an organism

5. Special emphasis attached to something

6. A point of convergence of light (or other radiation) or a point from which it diverges

7. A fixed reference point on the concave side of a conic section