ACARS (aircraft communications addressing and reporting system) is a data communications system which allows flight information to be transmitted between individual aircraft and the company host computer. These communications utilize various providers and communications mediums depending on aircraft equipment and current position.
ACARS is designed for domestic and international use. The system will automatically scan for VHF communications and will automatically utilize any available authorized air/ground system depending on aircraft position.
Typical usage involves receiving your PDC (ATC pre departure clearance), weather updates, ATIS in text format, automatically sending block out time, off time, on time and block in times to the company, text communications with your dispatcher or maintenance and position reports. It's alot like instant messaging with the company. Many ACARS equipped aircraft also have printers.
I dont remember what the letters stand for I am sure one of the pro guys can but its a computer that helps keep track of flight time (such as out of gate, off the ground, and eta). I know it also keeps a log of PF/PNF legs. If I am not mistaken it can also be used for mtc recordings. I know when I was a load agent we would get the crew to flip on the beacon so that it would show the flight out. Gotta show you pushed on time. ACARS can also but use to send messages to flight control and other people. Acts kinda like a Instant Messenger. Thats my take on does anyone else have more or am I way out in left field?