Multisignature arrangements are covered in full under Multi-Sig Wallet. "Multisignature" is simply the one-word spelling of multi-signature, and both refer to the same technique: funds can move only when a set number of keyholders sign.
The practical appeal of multisignature control is that it mirrors rules organisations already follow offline. A company that requires two directors to sign large cheques, or a bank that applies maker-checker controls so that one person enters a payment and another approves it, is applying the same idea. Crypto firms, investment funds and DAOs hold their treasuries in multisignature wallets so that no single employee, founder or compromised device can move funds alone. Individuals use them too, keeping keys in different places so that losing one does not mean losing everything.
Multisignature should not be confused with multi-factor authentication, which asks one person to prove their identity in several ways, such as a password plus a code. Multisignature instead requires agreement from several separate keys, which may belong to different people. A further alternative, the MPC wallet, spreads control by splitting a single key rather than requiring several signatures, and some custody providers combine both methods for extra safety.