I believe a commando is someone who can operate individually as well as part of a team. Commandos were designed for hit and run type missions. Royal Marines were designed to fight on/from Naval vessels.
A commando is an Irregular warfare/guerilla fighter and conduct raids/shock movements upon an enemy force. They are meant to sneak in, cause destruction and panic amongst the enemy then get out.
Unlike regular combat infantry they have to usually operate out of support range, thus they must carry with them everything they could need to complete there task and operate in remote/hard to reach areas.
Commando is indeed a South African word, Afrikaans (dutch dialect) specifically. Instructions were given to essentially militia from command and those receiving it were called a command-o (yes rather unglamorous i know). The name was selected out of respect for how these groups of basically farmers that had a good knowledge of the local terrain, horsemanship and marksmanship skills caused massive damage to the British forces during the boer wars.
There has actually been a good number of threads and disscussions on this topic i can dig em up if anyone would like