Laboratory Response Network, a collaborative effort of the U.S. Centers for Disease Control and Prevention and the Association of Public Health Laboratories
Laparoscopic radical nephrectomy, a medical procedure
Lateral reticular nucleus, a nucleus of the medulla oblongata involved with co-ordinating baroreceptor signals to control arterial blood pressure
Legislative route number, a designation for a highway defined by laws passed in a state legislature
Location Routing Number, a ten digit phone number used to route phone calls between two telephone exchanges
LORAN, a terrestrial radio navigation system originally known as LRN for Loomis Radio Navigation
LRN (company), an ethics compliance and education company
Luminous red nova, a stellar explosion thought to be caused by the merger of two stars