1. A girl aspiring to become your girlfriend.

2. The Girl that a guy keeps around in waiting as a back-up to his current girlfriend. Similar to a Sancha or the other woman, however calling a girl a redshirt girlfriend does not neccessarily imply that she has had relations with the guy while he was with the previous girlfriend.

etymology: a Redshirt Freshman is an american college football term for an athlete who practices with the team, but sees little game time in order save a year of eligibility to play for his team at a later date.
Definition 1- Man, that girl Kelly is all over you dude. I think she is your Redshirt girlfriend.

No one knew why Billy dropped his girlfriend Sally until everyone found out about his Redshirt Girlfriend, Gloria.
by The Mahatma December 26, 2008
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The woman on the sideline ready to jump in the sheets during the week that your wife or girlfriend is on the rag. Similar to a Sancha or the other woman.
Man my girl's ragging again. Time to hit up the Redshirt girlfriend.
by HOLEEFUKS October 1, 2015
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