Multi-signature addresses are like joint bank accounts, and are partially owned by each person who put forward a key to create it. When creating a multi-signature address, you need to specify how many of the owners need to sign to release the funds.
The Case for Multisig
You could set up an account between you and your wife that both of you can spend from, by creating a 1 of 2 address. This means: of the two keys used to create this address, a signature from only one party is required. Any money that was sent to this address could be spent by either party.
If you wanted to create a joint account, but wanted to approve transactions before the other person can spent money, you can create a 2 of 2 address. Of the two keys used to create the address, a signature from both is required. Both people who partially own the address can create unsigned transactions, and sign them with their own key, but without a signature from the second party, the transaction cannot go through. This could be the savings account you have with your wife, or maybe your wallet on another website. If one of you gets hacked, you still need the other to approve payments.
You can generate addresses with up to twenty possible signatories. So you could have a 5 of 10 address, where 5 people of the 10 need to agree on where the funds are going. This is pretty arbitrary until you find a purpose for your address.
One of the interesting cases is a 2-of-3 signature address, which allows for funds to be safely locked in escrow. If two people wish to perform a transaction (like purchase of goods, or services), but both parties fear that the other might not be trust-worthy, they can elect a trusted 3rd party as a signatory. If either party reneges on the agreement, the third party can create a transaction paying the money to the deserving party.
About MultiSig and how it works.
. But waiting for reply from а "Full Member". 
