Multisig means it takes more than one key to move your bitcoin. A common setup is "2-of-3": three keys exist, and any two can sign.
Go deeperMultisig protects you from a single point of failure. Lose one key and you can still recover with the other two; a thief who steals one key can't take anything. The trade-off is more setup and more to back up, including the wallet's configuration file, not just the seeds.