A
California roll, in my
experience, may be any
norimaki which is both a "
reverse maki" (
i.e. has
rice on the
outside) and contains
avocado and
crabmeat. It may well contain other things; I've seen a rather overstuffed
futomaki with crab, avocado, egg, and tofu advertised as a
California roll.
The interesting thing about the California roll is that it is supposedly the first variety of sushi invented outside of Japan which also subsequently became popular in Japan -- or, at least, in Tokyo.