A multisig wallet requires more than one private key to authorize a transaction, such as two of three keys. This removes the single point of failure of one key.
You create a wallet that needs signatures from multiple keys held in different places. A transaction only goes through when the required number of keys sign it.
No single stolen or lost key can drain or lock the wallet. Multisig is popular for shared funds, businesses and advanced personal security.
Multisig is more complex to set up and recover, and transaction fees can be slightly higher. It is overkill for small holdings.
Multisig is worth considering for large holdings or shared custody. For most individual holders, a hardware wallet with a secure seed backup is enough.