The day when all the money due to the seller is paid by the buyer, through the solicitors and you can collect the keys is known as the day of completion. This date is usually a pre-arranged date agreed at the time when the contracts were exchanged.
On this day, the legal ownership of the property is transferred from the seller to the buyer. The buyer will become the new owner of the property.
The seller will need to vacate the property and the keys will need to be made available to the property buyer.