In everyday language, a generalization is defined as a broad statement or an idea that is applied to a group of people or things. Often, generalizations are not entirely true, because there are usually examples of individuals or situations wherein the generalization does not apply. In this respect, generalizations can be similar to stereotypes in that they are sometimes offensive.
These are just a few of the many examples of generalizations that exist. As you can see, a generalization is a statement that is often true, but not completely true in all cases. Next time you find yourself making an overly broad statement about a topic or a group of people, stop and think about whether you are making a generalization yourself and if you are sure that's what you want to do.