NFT stands for non-fungible token, a type of smart property. They initially saw mainstream success with CryptoKitties and have since taken over popular culture; some of the world's most famous artists have begun tokenizing their work, and many celebrities are now producing their own. The most popular NFT platforms are Ethereum, Flow, and WAX.
Fungibility refers to whether or not all assets in a set are interchangeable. For example, while one US dollar is equal in value to another, one acre of land varies in value according to its location. Fungible assets are generally more liquid (easier to sell) than non-fungible assets, since buyers can be less picky about which specific token they are getting or from whom. Non-fungible tokens have more information about them, including off-chain files (such as image files for art) and on-chain metadata, which differentiates them from one another.
NFTs are the most widely recognizable implementation of the true ownership concept; blockchain-based collectible pets, items or trading cards are considered NFTs because they have varying names, artwork and attributes. Blockchain games commonly presell them before launch in order to raise funds for development, instead of or in addition to an ICO. Some of the most valuable NFT sales have been of land in blockchain games such as Axie Infinity, Decentraland, and Mirandus.