Strong Female Character is, first of all, beautiful. She is invariably sexually attractive, or whatever the equivalent in the universe of the story would be. She is also decidedly heterosexual. But SFC doesn't have time for romance, because she has been hurt before or she is too focused on her work, whatever it is. She has many layers of emotional defense, she doesn't let anyone get too close. But deep down she just wants to be loved. There is a vulnerability to her, and probably only Male Protagonist can see it.

SFC is hyper-competent. She's good at everything and not to be challenged. She has no time for frivolity or distraction. She is generally liked, though clearly not someone you would want to go to a discotheque with (can you tell how hip and happening I am?) - which is to say she's not much fun. She's very focused and determined and not about to let any obstacles stand in her way. She certainly isn't funny.

However, she does not save the day. Sure, she's integral to the day-saving, it couldn't have been done without her, but she is not the hero of the story. She will probably even need to be rescued at some point. And unless she's lucky she will act as Male Protagonist's emotional reward for overcoming whatever he overcomes over the course of the story. Because he's the first person who really gets her. He's the first person who can see beyond her hard outer shell and into her fleshy underbelly.

A few examples of SFC, from across genres, include Neytiri from Avatar, the lady car from Cars, Astrid from How to Train Your Dragon, Sif from Thor, and Irene Adler from Sherlock. Now, these aren't necessarily poor characters in isolation (except the lady car from Cars). But I could go on with this list. Strong Female Character is everywhere. I am very tired of her.

Strong Female Character is a problem because she allows people to think women are now being written into films and TV appropriately. "Look, we're not making women weak and useless!" Well, yes. But that was not the only problem with the way women have been traditionally written in mass media fiction. It's a big problem, certainly, but another underlying problem is the way women are written as basically all the same. There are women who are very much like Strong Female Character, but there are many many more women who are not. Frankly, there are weak and useless women, too. The point is that women are many and varied and female characters should be, too. All that said...

Strong Female Character is a necessary step between terrible representations of women and good representations of women. The first few times SFC showed up she was probably very exciting. She should be in the process of being phased out, but I think the reason she's still around is because she feels safe. When you're making a movie, you only have time to develop so many characters. If you've decided that only one of your main characters can be female (which is a problem in and of itself), you become limited in the current climate of gender equality. If you give your one female character a flaw, you seem to be saying that all women have that flaw. So you have to make her flawless. The solution to this problem is obvious - have more than one prominent female character. They have to be different, so at least one of them can't be Strong Female Character. Jane and Darcy are able to be interesting because Sif is already taking up the SFC slot.