Most Helpful Girl
This is a common misconception. Leggings are definitely NOT pants. Ever. Seriously.
Some people do wear them as pants. I personally don't think it's a flattering look for anyone. Leggings were designed to be worn under other clothing such as skirts or certain types of dresses. The function of leggings is much like the function of tights or panty hose, yet you don't see girls trying to wear THOSE as pants, now do you.
The material is thinner than that used for any type of actual pants and can often be somewhat see through by itself. They are also made to be skin tight, which is alright I guess if you have a fantastic body, but for the average person (including many thin/in-shape women) it just looks tacky.
Jeggings are a completely different story. They are designed to be worn by themselves, as a response to the leggings-as-pants trend, therefore they are slightly thicker and fit a little differently. Although I personally still think they look dumb for the most part, at least they are real pants.