I looked around in the P&T forum, and was surprised that no one had posted a topic / thread about it.
In my own words, individualism is similar to objectivism, but specifically revolves around yourself. Individualism is (obviously) all about being yourself and being independet, hence "individualism". The "downside" to this (some people believe) is selfishness; some individualists argue that selfishness is a virtue, while others think it is not a good thing to inherit (though what is "good", honestly?).
There's also a lot on egoism, but personally, I like to think that being an individualist is about thinking for yourself, making your own "good" choices (and not ALWAYS having to justify why you did it), and (in relation to reason #1), believing what you believe because you think it is rational.