Young Teen Girl In Tight Pants

In the United Kingdom and Ireland most people use trousers or slacks as the general category term, whereas pants usually refers to underwear but is used, interchangeably with trousers, in some northern dialects. In Scotland, trousers are known as trews, which is the historic root of the word 'trousers'. Trousers are known as breeks in Scots.
In North America pants is the general category term (though Ambrose Bierce found the word "vulgar exceedingly" and recommended trousers), whereas trousers (sometimes slacks in Australia, the United States,) often more formally, to tailored garments with a waistband and (typically) belt-loops and a fly-front. For instance, informal elastic-waist knitted garments would be called pants, but not slacks.
North Americans call undergarments underwear, underpants, "captain underpants", "long johns" or panties (the last are women's garments specifically) to distinguish them from other pants that are worn on the outside. The term drawers normally refers to undergarments, but in some dialects, may be found as a synonym for "breeches", that is, trousers. In these dialects, the term underdrawers is used for undergarments. In Australia, men's undergarments are called underwear, underpants, undies, under-dacks, dacks or jocks.
Various people in the fashion industry use the word pant instead of pants. This is nonstandard usage. The word "pants" is a plurale tantum, always in plural form—much like the words "scissors" and "tongs". However, the singular form of the word is used in some compound words, such as trouser-leg, trouser-press and trouser-bottoms.