Daguerre is a circular formation near the north end of Mare Nectaris. To the west-northwest is the crater Mädler, and beyond it to the west is the prominent Theophilus. To the north in the rugged continental area between the maria is Isidorus. This feature has the appearance of a lunar crater that has been nearly submerged by a lava flow, leaving a gap in the southwest wall that gives the feature the shape of a horse-shoe. (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.