Many Scuba divers choose to use open heel fins for diving and therefore need booties to slide into the fin pocket.
The booties also provide protection for the feet when walking on the hot beach sand or from knocking your toes on the boat as well as also provide warmth for the feet while diving.
You can get a high cut booties or a low cut bootie. This generally refers to how high they sit on the ankle.
Neoprene Socks are excellent to use with closed heel fins and free-diving fins, to keep your feet warm.

Gloves are also added for additional warmth especially when diving in colder waters.