The Locking Spell (incantation, Colloportus) is a charm that is used to lock or seal doors so that they cannot be opened manually. This charm is featured in  The Standard Book of Spells, Grade 1 and has a very well-known counter charm, Alohomora.

It is unknown whether a key could be used to unlock a door after a locking charm has been placed on it.. If it is true that a key would be ineffective against a door sealed with this spell, it would prove quite useful against Muggles.