Token is a unit of value issued by a tech or crypto start-up, intended to be a piece in the ecosystem of their technology platform or project. Tokens are supported by blockchains. They only physically exist in the form of registry entries in said blockchain. Initially, most tokens were based on the ERC20 protocol by Ethereum.
Tokens are different from bitcoins and altcoins in that they are not mined by their owners nor primarily meant to be traded (although they may be traded on exchanges if the company that issued them becomes valuable enough in the eyes of the public), but to be sold for fiat or cryptocurrency in order to fund the start-up’s tech project.