The 180 is the semi-auto version of the AR-18. A select fire 5.56 mm that was designed to be more easily manufactured in third world nations. It is made with sheet metal stampings rather than expensive aluminum forgings (M-16). The 180 uses a gas piston system not unlike the AK's. The folding stock, Z shaped cocking handle and lack of carry handle being the most visible differences.
The early versions were made in Japan and England. The new rendition uses a polymer lower receiver and lacks the folding stock (I believe).