A multisignature wallet requires several keys to authorise a transfer rather than one. The rule is enforced by the chain rather than by an application, which is what gives it force.
The quorum is a condition on spending
A multisig address is controlled by a script or contract that accepts a transaction only if a defined number of listed keys have signed it.
The arrangement is written as m-of-n: three of five, two of three. Any m signatures satisfy the condition and the rest are ignored.
Because the check happens where funds settle, no operator can waive it. There is no support desk that can approve a transfer without the signatures.
Separation is what produces the security
The benefit comes from keys that do not share a failure. Different devices, different locations, different people, different ways of being backed up.
Five keys on one laptop is a single key with extra steps. The compromise of that laptop takes all of them at once.
Separation also raises the cost of coercion, since a single person under pressure cannot produce a valid transaction alone.
The threshold trades theft risk against loss risk
Raising m makes theft harder because more keys must be captured. It also makes permanent loss more likely, because fewer keys may be misplaced before spending becomes impossible.
Raising n relative to m does the opposite: more spare keys exist, so loss is survivable, but the pool an attacker can draw from is larger.
There is no configuration that minimises both risks at once, which is why the right threshold depends on whether the greater danger is a break-in or a forgotten backup in a drawer.
What it costs in practice
Every transfer needs coordination. Signers must be reachable, must be running compatible software, and must review the same unsigned transaction before it can be broadcast.
On chains that charge by data, multisig transactions are larger and cost more, since several signatures and the spending conditions travel with them.
Recovery is also more involved. Restoring a multisig wallet requires the spending policy as well as the keys, and a set of seed phrases with no record of the arrangement they belonged to can be unusable.
The failure it does not fix
Multisig protects the keys, not the judgement of the people holding them. If every signer approves the same malicious transaction, the quorum is satisfied and the funds leave.
Attacks against organisations therefore target the process rather than the cryptography, presenting each signer with a transaction that looks routine in the interface they are used to.
That is why signing devices that display transaction details matter as much as the quorum. Signers who cannot read what they are approving are approving whatever the interface tells them.