Someone who knows a lot about a particular subject and loves learning more about it is called a buff. If your friend can name every dinosaur species and explain how they lived, she's a dinosaur buff. If your uncle collects old coins, studies their history, and can tell you which ones are rare, he's a coin buff.

The word suggests passionate knowledge that goes beyond casual interest. Someone who enjoys watching movies is a moviegoer, but a film buff studies directors, remembers obscure details, and gets excited discussing camera techniques. History buffs go deep: they read biographies, visit museums, and connect events to understand how the past shaped the present.

Being a buff means you've gone beyond homework-level knowledge into genuine enthusiasm. You might become a baseball buff by collecting cards, learning statistics, and watching old games. The key is that you're learning because you want to.

The word can describe expertise in almost anything: art, trains, military history, cooking, you name it. What makes someone a buff is their enthusiasm for knowing more, combined with the depth of knowledge they've built.