It is the cryptocurrency disbursed to one or more addresses as a result of a transaction. The transaction received an input of currency which is used in part to pay for the transaction itself and then split and sent to the address(es) of the recipient(s). The output of a transaction can only be the input of another subsequent transaction. In this way, the money flows from a transaction to another without ever leaving the blockchain.
There are two types of output: spent transaction outputs and Unspent Transaction Outputs (UTXO). Only UTXOs can be used as the input for a new transaction.
If the output of a transaction is bigger than its input, the transaction will be rejected.