On Strong Female Characters in Red Phone Box

It's been on my mind a lot lately.

What makes a character strong? I don't think there's a single, straightforward answer to that. Are characters weak if they cry? Do they need to be physically strong? Do they need to be fearless?

I guess I feel there are many kinds of strength. There's physical strength, as in the power-lifting kind. Women are usually going to be at a slight disadvantage in this area because of simple size and muscle density reality. But there are many other factors to streng...