What does it mean when someone has a "glass jaw"?

I think it's when they clench their teeth and you can see their jaw more but I'm not sure. What does it mean?

what does it mean when someone says I gave him the means to the ends?

What does it mean if you rep someone? Just wondering..

What does it mean when someone says your first on the bad list, and you're last on mine

what does it mean when someone say I think the fruit is rotten? as in the saying

What does it mean when someone says he's 2 years her senior? Or he's 2 years her junior? just wondered :)

what does it mean when someone says back roads always lead to something?

What does it mean when someone says against the grain should be a way of life

what does it mean when someone says that you have a hollow voice or that it sounds hollow?

What does it mean when someone says your first on the bad list, and you're last on mine