A multipoint lock is one that locks the door at several points at once with a single key. Instead of holding it only at handle height, it throws bolts at the top, at the bottom or at several points along the side.
The advantage is clear: if someone tries to lever it, the force is spread across the whole door and there is no single weak point. It is what many security doors have, and also many aluminium and uPVC doors, such as patio doors.
Day to day nothing changes: you open and lock with the same key. What it does need is a well adjusted door, because if the frame moves, the bolts stop going in properly and it becomes hard to lock.
It can be fitted on many doors that have a simple lock today. We look at it in multipoint locks.