A crypto token is an asset based on the blockchain of another asset, which is called a coin. Part of the definition of tokens is that they do not run on their own blockchains — a key distinction in clearing up the token vs. coin confusion.
Projects often build solutions on existing networks, such as Ethereum. Ethereum has a coin, called Ether (ETH), running on its blockchain. The majority of the tokens built on the Ethereum blockchain are ERC-20 tokens, or ERC-721 tokens if they are nonfungible tokens, or NFTs.
Each project typically employs its own token, meaning that the token runs on the blockchain on which the project was built. An entity can create a cryptocurrency token for a number of reasons, including use within a broader ecosystem. ICO tokens were popular during the initial coin offering boom of 2017.