NFT stands for ''Non-fungible token''.
“Non-fungible” more or less means that it’s unique and can’t be replaced with something else. For example, a bitcoin is fungible — trade one for another bitcoin, and you’ll have exactly the same thing. A one-of-a-kind trading card, however, is non-fungible. If you traded it for a different card, you’d have something completely different. You gave up a Squirtle, and got a 1909 T206 Honus Wagner, which StadiumTalk calls “the Mona Lisa of baseball cards.”
At a very high level, most NFTs are part of the Ethereum blockchain. Ethereum is a cryptocurrency, like bitcoin or dogecoin, but its blockchain also supports these NFTs, which store extra information that makes them work differently from, say, an ETH coin. It is worth noting that other blockchains can implement their own versions of NFTs.
NFTs are designed to give you something that can’t be copied: ownership of the work (though the artist can still retain the copyright and reproduction rights, just like with physical artwork). To put it in terms of physical art collecting: anyone can buy a Monet print. But only one person can own the original.
One of the obvious benefits of buying art is it lets you financially support artists you like, and that’s true with NFTs (which are way trendier than, like, Telegram stickers). Buying an NFT also usually gets you some basic usage rights, like being able to post the image online or set it as your profile picture. Plus, of course, there are bragging rights that you own the art, with a blockchain entry to back it up.
In the boring, technical sense that every NFT is a unique token on the blockchain. But while it could be like a van Gogh, where there’s only one definitive actual version, it could also be like a trading card, where there’s 50 or hundreds of numbered copies of the same artwork.