A memory wipe was a medical procedure designed for the purpose of selectively eliminating memory engrams from the mind of an individual. It was different from a memory block, in which the memory was merely supressed.
Dr. Katherine Pulaski developed a memory wipe technique which was effective on many humanoid species. It was used on Sarjenka, a young girl from the pre-warp civilization on Drema IV, in order to prevent her from telling her people of her experiences with the Enterprise. (TNG: "Pen Pals")