Leggings www.teesbytina.com/.../textured-leggings.jpg thicker than tights, don't have the sock part. You can wear them with pretty much anything, but i prefer longer tops, since I'm not really a fan of showing off my butt XD
@SomeGuy37 - as a recent thong undies wearer I and a whole lot of other Ladies can assure you that thongs are both comfortable and sensible undies. They look better (to us) than a pair of boyshorts (the other style that's comfortable to me) under yogapants. We don't like advertising our undies beneath yogapants or any other form fitting attire, we wear them for ourselves not ogling men. Rather see a woman wearing a thong under those yogapants than nothing.
Tights have feet and are usually somewhat see through Leggings are cut off at the feet thicker and if you get the right ones aren't see through Yoga pants usually have a thicker band at the top and a lot of the time in a sports fabric, also cut off at the feet.
Leggings and yoga pants are almost the same thing except yoga pants usually come in more of a bootcut fit. It's best to wear a thong or seamless underwear with leggings or yoga pants. Neither of these would be good for work except for the case of working somewhere with a very casual dress code. Tights should really only be worn under a dress or skirt since they are more see-through than yoga pants or leggings. The kind of underwear worn with tights pretty much just depends on the dress or skirt that is worn with the tights. Tights are fine for work if worn with a professional looking skirt or dress.