A single signature wallet, or singlesig for short, is a type of wallet that requires only a single private key to sign transactions. This setup is considered the standard for any basic wallet because knowledge of the private key implies full control over the bitcoin held in the wallet.
Transitioning to a multisig wallet means the addition of more keys, and this, in turn, demands that the owner writes down, stores, and keeps another private key confidential. The majority of Bitcoin wallets are singlesig type. These wallets are the most convenient for transactions, and provided the user securely maintains the private key, ideally in conjunction with a password or pin, they offer sufficient security even for storing substantial wealth.