Ingroup bias is a simple concept, but one that has very powerful affects on people, societies, and life in general. Ingroup bias is simply the tendency to favor one's own group. This is not one group in particular, but whatever group you associate with at a particular time. So, for example, when you play on an intramural softball team that meets once a week, you are part of that softball team's ingroup. Or, it can be something on a much more grand scale like, the situation between religious groups in Ireland. They have been killing each other for years, because they each perceive their own group as being the "right" and "good" group, while the other group (the outgroup) is "bad" and "evil".