ERC-20
The most widely used Ethereum standard for interchangeable tokens, defining how balances are read and transfers are authorized.
ERC-20 specifies a small interface: total supply, balance of an address, direct transfer, an allowance one address grants another, and the transfer that spends that allowance, plus events announcing both. The allowance pattern is why applications ask permission to spend your tokens before a swap or a deposit, and why standing unlimited approvals are a persistent security exposure that wallets now let users revoke. The standard says nothing about supply policy, so whether new units can be minted, burned, or frozen depends entirely on the individual contract. The interface has been copied by other chains that run the Ethereum Virtual Machine, so the same token code appears across many networks.
In practice
When a decentralized exchange asks for permission before your first swap of a token, it is calling that token's ERC-20 approve function.
The common misunderstanding
ERC-20 tokens are not stored inside your wallet: the balance is a row inside the token contract keyed to your address, which is why the token exists only as long as its contract does.