Tokens are the T in NFTs. Generally, these are the things that are sent between wallets. On Solana, they are the product of the Token Program. Anyone can create a new token, by sending a transaction with instructions for creating the token to the Token Program. This program then creates a new Account with the necessary information about the token and ownership of that account is assigned to the wallet that sent the transaction. Now, the creator can do what they want with their tokens. Tokens can be made Non Fungible, to complete the NFT acronym, by making them unique in some way. This is usually done by associating metadata with each token, which can contain a unique identifier, for example.