A memory wipe is a medical procedure designed to selectively eliminate memory engrams from the mind of an individual.
Dr. Katherine Pulaski developed a technique which was effective on a large variety of humanoids. It was used on Sarjenka, a young girl from the prewarp civilization on Drema IV, in order to prevent her from telling her people of her experiences with the Enterprise. (TNG: "Pen Pals") The technique was not successful on all humanoids, however. Mintakans were unaffected by the memory wipe (TNG: "Who Watches the Watchers?"), as were the Boraalans (TNG: "Homeward").
A memory wipe was used by Dr. Julian Bashir to reassign Kurn's identity to Rodek in 2372. (DS9: "Sons of Mogh")