Deposit is defined as money given to a bank who then guarantees its security. However, when someone deposits cryptocurrency, they are not transferring the money. They are actually transferring ownership and access of their crypto.
Most people who want to trade their cryptocurrency for another type use what is called an exchange. When a user deposits crypto into an exchange, what they are actually doing is transferring their ownership and access of the crypto to the exchange. In other words, they are cancelling their private keys and completely turning over their access to the exchange’s private keys.
Most exchanges are very trustworthy, but some are not. It is thought that most exchanges would reimburse you if they lost your crypto. But no exchange is required by law to do that. When you deposit your crypto, you are fully entrusting them to keep it safe.