The point at which a purchaser is legally obliged to buy at the price and the vendor is legally obliged to sell to the purchaser. A deposit is generally paid and a future completion date is fixed.
this is the day when contracts between buyer and seller are signed and swapped by the solicitors. The sale becomes certain. After this point, if either party wants to pull out, they must compensate the other.
The point at which both buying and selling parties sign their copies of the contract. They are then exchanged by the respective solicitors. The agreement to buy and sell is then binding. The buyer usually pays a deposit at this point and the completion date is agreed.