A Memory Charm is a spell used to erase some or all memories from an individual's mind. The incantation for such a charm is Obliviate.
There are varying degrees in the power of Memory Charms. Some only erase a specific memory (such as that which Kingsley Shacklebolt used on Marietta Edgecombe to prevent her from talking about secret Dumbledore's Army meetings). Others, if not performed by a trained professional, can be strong enough to cause brain damage. For instance, Gilderoy Lockhart attempted to Obliviate the memories of Harry Potter and Ron Weasley during the events surrounding the re-opening of the Chamber of Secrets, however, Ron's damaged wand backfired and caused Lockhart's extreme amnesia. He is currently a resident in the Permanent Ward of St Mungo's.
Memory Charms may wear off if they are not performed properly. Bartemius Crouch attempted to keep his delinquent son under house arrest with a Memory Charm, but he broke free in time.
Memory Charms may be broken through torture. Lord Voldemort and Peter Pettigrew broke a Memory Charm placed by Barty Crouch Sr on Bertha Jorkins, and extracted information from her regarding the whereabouts of Crouch's son.
in 1997, Hermione Granger performs Memory Charms on Death Eaters Antonin Dolohov and Thorfinn Rowle after they ambushed her, Harry and Ron in a cafe at Tottenham Court Road, as well as the Muggle waitress who witnessed the skirmish.
Behind the scenes
Hermione had also altered her parents' memories, despite saying that she had never done a Memory Charm before. However, J.K. Rowling has said this was a different charm.