Internally (in the server and over the wire, i.e. in GRPC requests) addresses are byte arrays with a length of 33. They represent the compressed public key of an account.
In the case of smart contracts, the address is generated from a hash of the creator’s account and the creating transaction’s nonce, prefixed with the byte 0x0C to arrive at a compatible length of 33 bytes. As a developer, you don’t have to worry about this: smart contract addresses can be used just the same as account addresses.
