Basic theory of expander graphs

This looks like it's from a special topics course Terry is teaching at UCLA:

http://www.math.ucla.edu/~tao/254b.1.12w/

The course description says the course assumes a familiarity with graduate-level mathematics.

These notes in particular look more accessible than that to me, provided you are willing to stop and research definitions.

This is an especially good find for several reasons. Terry's explanations are excellent, he rarely writes at an introductory level, and expander graphs are quickly becoming a central topic in math and computer science.