Mopar is a registered slang nickname for Chrysler Corporation car parts and sometimes cars themselves [mostly Chrysler, Dodge, Plymouth and AMC after 1987, less popular term for Imperial, DeSoto and Jeep makes]. This word simply stands for “motor parts” abbreviation.
After Chrysler bought Dodge in 1928 there was a need to set up a dedicated parts supplier. So, in 1929, “Chrysler Motor Parts Corporation” was established [CMPC]. Firstly, Mopar started as a line of antifreeze products, but in the muscle car era, 60s-70s, Mopar was high-performace parts for Dodge and Plymouth including super-stock parts for drag racers. There was also a “Mopar Performance Parts” division established for parts developing.