To pertain means to relate to something or be connected to it. When a question pertains to your homework, it has to do with your homework. When a rule pertains to fifth graders, it applies to fifth graders specifically.

You'll often see this word in more formal contexts. A teacher might say that her comments pertain to the essay you wrote, meaning they're about that essay and not something else. A lawyer might point out that certain evidence doesn't pertain to the case, meaning it's not relevant or connected to what's being decided.

Think of pertain as a way to draw a clear line between what belongs to a topic and what doesn't. If you're reading a book about ancient Egypt and someone asks a question about the Roman Empire, you might say that question doesn't pertain to what you're studying. The word helps you stay focused on what actually matters for the subject at hand.

Pertain is closely related to the word pertinent, which describes something that pertains to the topic: a pertinent question is one that relates directly to what you're discussing.