Glossary
Exchange
A company that matches buyers and sellers, and often holds coins for them.
A centralised exchange is a business with an app, a helpdesk, and a set of wallets it controls. Your balance there is usually an IOU in their database, not coins only you can sign. Password resets exist because they hold the keys.
That is convenient until the company pauses withdrawals, gets hacked, or goes bankrupt. An exchange can still be a reasonable on-ramp. It is not the same as self-custody.
