"I will jump in and take out Loki and his subordinates. Then, I will go home and prepare dinner."
The Action Girl is a female Badass who can go toe to toe with her male counterparts without breaking a sweat. Damsel in Distress? Not for this babe. She doesn't sit around waiting to be rescued. She's headbutting her jailer and breaking herself out. She proves, with her very being, that girls aren't only not helpless, they kick ass. But not just "any girl with a fight scene" can be considered an Action Girl. An Action Girl is accompanied by Rule of Cool, and routinely and reliably gets in on the combat. And what's more, she wins.
Because of Double Standards, true Action Girls are less common than male Badasses. If you want to get more into the why of that, check out the Gender Dynamics Index or our very own Action Girl Analysis page. The short version however, is the concept that Men Are Strong, Women Are Pretty and females should Stay in the Kitchen. For a very long time, females who did much but wait around for their hero to come rescue them were unusual and rare. Even now, women aren't automatically assumed to be able to fight and protect themselves the way men are. Society has progressed since then and Action Girls are popular and more common than ever, but girls still haven't completely caught up with boys when it comes to expectations in media, hence the continued existence of this trope.