Individualism is not to be confused with selfishness or the general usage of the word “egotism”.
a) The difference between individualism and SELFISHNESS is that individualism recognizes that other people are individuals too, just like oneself. Selfishness on the other hand is not such a consciously held conviction. In fact, selfishness is the absence of any conviction with regard to how you relate to other people. *
b) The difference between individualism and ALTRUISM is that altruism considers that OTHERS are individuals, but somehow, strangely, oneself is not. To paraphrase, “If I’m here to help others, what on Earth are others here for?”
c) The difference between individualism and COLLECTIVISM is that individualism holds that every individual is just as important as every other individual, whereas collectivism holds that the group is more important than any individual who makes up that group. Or more generally, where M > N, the wishes of M individuals are more important than the wishes of N individuals.
* i.e. individualism is a philosophical position; selfishness is just a bad habit.