A blood bank was a facility where emergency supplies of blood were collected and stored.
Loomis was employed at a blood bank located in Porter Street in Detroit, Michigan in 2004. The supervisor at that specific facility was considered by Loomis to a "fat broad".
During his time employed at the blood bank, Loomis used records of the blood bank's clientele to acquire eight samples of Human blood for use in creating a Xindi bio-weapon. (ENT: "Carpenter Street")
The USS Enterprise also had a blood bank. In 2268, Christine Chapel checked the blood bank for Vulcan blood and plasma and found insufficient quantities for Ambassador Sarek's operation, thus necessitating his son Spock's cooperation. (TOS: "Journey to Babel")