What's skinny to someone else might not be skinny to me, and vise versa. So you can't just slap a standard on skinny legs. But I would go as far as to say, if you think you might have skinny legs, then you probably have skinny legs. But don't look for a standard on what's what. If you're okay with your leg size, good for you. If you want bigger legs, go for it. If you're happy with your leg development and someone's pounding you about it, **** them! lol
The remedy for skinny legs include heavy squats, heavy leg presses, hack squats, front squats, lunges, and leg curls. There are other good exercises, but these are usually at the top of most people's lists. Calve training is also important because if you neglect to train your calves, like I once did, you find that your thighs can develop out of proportion to your lower legs.
So the key to great success with your legs is heavy, consistent, quality training. Maintaining an appropriate diet for your goals should be a no-brainer. Also, don't neglect to train the endurance aspect of your leg muscles. The legs are capable of great strength and great endurance: no other muscles can do the same. Take advantage of that! If you train your legs with heavy weight and also train for increased leg endurance, you will see results.