NFT stands for...
Not Fungible Token.
Let's immediately clarify the meaning of fungible and non-fungible:
FUNGIBLE:
Think about like normal money.
The cryptocurrencies, Bitcoin, Ethereum or Mana for example, are fungible because are replaceable with other cryptocurrencies in exchange plattform. Just like normal money, you can "replace" crypto currencies with other crypto currencies or use it buyng some real or digital product.
That's why we say "fungible": Usable to purchase goods or products and replaceable with similar in equal value.
NOT FUNGIBLE:
Think about like normal product.
NFT is "a product" (digital product) that you can buy or sell, donate it for free, make a trade for money or another NFT, but not replace it because NFT is an unique piece. NFT has its own unique code which never changes and which will always identify that specific piece of digital product created on the internet. NFT is a single product which may also have copies, but they will never have the same identification code.
That's why we say "not fungible": Not usable to purchase goods or product and not replaceable.
And here we also explain why we write "NFT" indicating a single piece or "NFTs" with the final es, to indicate the plural if we are talking about several pieces.
Very helpful!