Short answer
A self-custodial wallet is one where you, and only you, control the private key that can move the funds. No company can freeze, lend out or spend your coins.
Every crypto wallet is really a key pair: a public address that people can send to, and a private key that signs transactions. Whoever holds the private key controls the money. With a self-custodial wallet, that key lives on your device or with a sign-in method only you can use, not on a company's servers.
The upside is independence. If an app shuts down, your coins are still on the blockchain and you can open them in any compatible wallet. Nobody can block a withdrawal because nothing was ever deposited with them.
The trade-off is responsibility. There is no password-reset desk for a private key. If you lose it and every backup, the funds are gone for good. Read what a seed phrase is and how to keep a wallet safe before you put in money you care about.
See the checks for yourself
18+ only. Self-custodial: you keep your keys. 0.5% per trade, no minimum. Memecoins can go to zero.