Named after Paul Hainzel - German astronomer (1527-1581).
Hainzel is the southern member of a trio of overlapping lunar craters. Hainzel forms the south portion of the grouping, and is overlain by Hainzel C to the northeast, and then by Hainzel A in the north. Hainzel A is the most intact and also the youngest of the cluster. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On the Moon they are named after deceased scientists, polar explorers, astronauts or cosmonauts.