focal point

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun optics A focus; a point at which rays of light or other radiation converge.
• noun The centre of any activity.
• noun art A feature that attracts particular attention.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a point of convergence of light (or other radiation) or a point from which it diverges
• noun the concentration of attention or energy on something
• noun a central point or locus of an infection in an organism