Meaning of NonFungible Token
This is a token that the whole or part of it cannot be interchangeable with another as a medium of payment or exchange of value. Let’s simplify this for you, if you own a pet (Cat) and fiat ($1,000 bill) and the Cat also worth the $1,000. If you want to purchase something worth $300.
You can easily drop your $1,000 bill and get a balance of $700 bill but you cannot decide to sell part of your Pet (Cat) and keep the other part as balance (like cutting off the head and keeping the other body part? – No!). Thus, your pet is Non-Fungible (examples includes ERC721 Tokens like Cryptokitty on Ethereum Blockchain).
See Fungible Token!