Prior means coming before something else in time or order. If you had a prior engagement on Saturday, that means you already had plans before someone invited you to do something new. If a judge asks about prior convictions, she wants to know about crimes committed before the current case.

The word helps us talk about sequence and timing. A teacher might say that finishing your math homework is prior to playing video games, meaning the homework comes first. Scientists talk about prior knowledge, the things you already understood before learning something new. When you read a mystery series, understanding the prior books helps you follow the later ones.

Prior can also describe importance or rank. A prior claim to something means you had the right to it first, before anyone else asked. If two students both want to use the art supplies but one reserved them yesterday, that student has the prior claim.

Notice that prior is more formal than simply saying “before” or “earlier.” You'd say “I read that book before” in casual conversation, but “I have prior experience with that author” sounds more official or serious.