A common motif in video games story's have the main character, or a supporting character, as a new, inexperienced addition to a team or squad. This character is generally trying constantly to prove his worth to his teammates, or peers. Usually by the end of the game, they were the most pivotal in the story, and the character has proven everybody wrong. On the other hand, the Gears of War series takes great delight in introducing rookie characters who are unceremoniously killed off by the end of the game as a running gag.
Another common term used for the rookie is "FNG" or "fucking new guy". This exact term is included in the Alliance Military Glossary in the Codex of Mass Effect, although to avoid being vulgar, the definition is given as "freaking" new guy, quotes included.