The rim or edge of a crater is the part that extends above the height of the local surface, usually in a circular or elliptical pattern. In a more specific sense, the rim may refer to the circular or elliptical edge that represents the uppermost tip of this raised portion. If there is no raised portion, the rim simply refers to the inside edge of the curve where the flat surface meets the curve of the crater bottom.
A side view of a crater, with a raised rim, highlighted in red.
This article about an extraterrestrial geological feature is a stub. You can help Wikipedia by expanding it.