Taking something specific and applying it more broadly is making a generalization. It's a generalization to say all dogs chase squirrels.
A generalization is taking one or a few facts and making a broader, more universal statement. If all the girls you know play with dolls, you might make the generalization that all girls play with dolls. Scientists try to make generalizations based on research — the more data they have, the more accurate the generalization. Generalizations can be similar to stereotypes in that they are sometimes wrong and harmful. Usually, it's best to stick with specifics and avoid generalizations.