In the context of the Bitcoin network, the term “change” pertains to the client’s generation of new Bitcoin address and the sending of the difference back to the address. This happens once the coin value of the output of a transaction is higher than what the user desires to pay.
Much like what happens with Fiat Currencies, when a user uses Bitcoins, he or she needs to use the entire value of an unspent output. This should then be made into the input for a new transaction. A user’s wallet hides this somewhat by continually searching for unspent outputs and adding up to their total value. For instance, when users see that their wallets have 10 BTC, what this tells them is that the sum of the unspent outputs is 10 BTC.