Like the air we breathe and the water we drink, underwear is a part of life  so ubiquitous that it often goes unnoticed. Don't let another year pass being unclear about your underpinnings — especially considering 99 percent of you are wearing them right now. (And if not, well, maybe you should be.)
We're exploring the wide yet sometimes very, very thin world of panties and breaking down the seven most common styles — sorry, no crotchless or C cups (we beg you not to Google Image search that) here.
Modeled after men's briefs, they take on a more rectangular shape than most panties. Similar to the hipster, the key difference is that they have a lower-cut leg. In fact, some styles' legs extend a short way down the thigh.
When to wear them: When fitted properly and made from the right fabric, boy shorts can actually serve the same function as a thong in being worn under formfitting clothes without visible panty lines. Longer cotton boy shorts, however, can even be worn as loungewear or pajamas.
Calvin Klein Modern Boyshorts  ($22)
H&M Microfiber and Lace Boy Short  ($8)
Free People Intimately Women's Eyelet Boyshort  ($18)
Uniqlo Boyshorts  ($5)
Commonly identified by the colloquial term "granny panties," this undergarment provides full coverage and a high waistband. Sure, it's not the most attractive style of underwear, but it's certainly the most comfortable.
When to wear them: Unfortunately, the up-to-the-navel waist makes these visible in low-rise jeans and trousers, so limit them to your high-waisted pants or for, you know, that time of the month.
Only Hearts 'Whisper' Cage Back Briefs  ($51)
BASERANGE Bell Two-Tone Cotton-Blend Crepe Briefs  ($65)
ASOS Geisha Lace High-Waisted Pant  ($17)
Jaded London High-Waist Underwear  ($41)
Often referred to as high-cut panties, these gained a resurgence in the 1980s, thanks to Jane Fonda's exercise videos. They have the same high waist as the classic brief, but it features high-cut leg holes that rise just above the widest part of the thigh, which is often better for circulation.
When to wear them: If you are Miley Cyrus . Or if you want the coverage of a brief but find the elastic band around the leg uncomfortable.
Jockey Seamless French Cut Underwear  ($10)
Undiz Equiliz String Underwear  ($12)
Magie Veda High Brief  ($125)
Wacoal Awareness Hi-Cut Underwear  ($8)
Not meant to be worn by hipsters alone, this style — also called hip huggers — got its name because the waistband sits on the hips, a full two inches below the waist. They also feature low-cut leg holes.
When to wear them: These still provide full coverage but are perfect for low-rise jeans and pants.
Calvin Klein Underwear Hipster With Lace  ($12)
Eberjey Bonnie Hipster  ($33)
Maidenform Smooth Luxe Comfort Lace Hipster Panties  ($12)
Aeropostale Hipster Underwear  ($9)
This pair of underwear is modeled after, naturally, women's bikini bottoms. The waistband sits a full three inches below the natural waist and has very high-cut leg holes. They also come in string bikini form, in which the leg holes are constructed with a thin string of fabric. The front and back of the string bikini look like triangles.
When to wear them: Because they provide little coverage, they are less visible underneath clothes and thus can be worn under most anything.
Stella McCartney Lace Bikini Briefs  ($56)
Xhilaration Micro Bikini With Lace  ($5)
Tommy Hilfiger Ruched Bikini  ($12)
OnGossamer Solid Gossamer Mesh Hip Bikini  ($16)
This is the style most often sought when needing an undergarment for formfitting clothing, like tight skirts or dresses, because it provides no coverage on the butt — and thus no panty lines. Like the bikini, it sits three inches below the waist. Often, the sides are meant to rest right at or above the hip bone.
When to wear them: Whenever you're in the mood to twerk to some Sisqó. Or when you're rocking a body-con dress or tight pants.
Versace Stretch Cotton Jersey Thong  ($72)
Hanky Panky Ruffled Low-Rise Thong  ($26)
DKNY 'Fusion' Thong  ($12)
Aerie Vintage Lace Thong  ($13)
There's little to the G-string panty. Like the thong, there's no rear coverage, and this style also provides little up front, where it forms a T shape of fabric. The front and back pieces attach directly to the waistband.
When to wear them: To your next hot date? Because thongs and even boy shorts often provide a seamless look underneath clothes, it's rarely necessary to require a G-string.
La Perla Sexy Town Mesh G-String  ($38)
DKNY G String  ($10)
Moschino G-String  ($49)
Cosabella Cheyenne G String  ($35)