Shorts

Shorts are short length trousers or pants that reach only to the upper part of the legs or more, but do not cover the entire leg. They are worn by both men and women.  Shorts are worn either as outer garments or as underwear. They are called "shorts" because they are a shortened version of trousers (as they are called in British English, or pants in American English) which cover the entire leg.

Why people wear shorts:
 Fashion  appearance, attractiveness
 Practical  cool, light weight, allows for ease of movement; sportswear
 Uniform  decided by the organisation the wearer belongs to

Types

There are many types of shorts:

 Boxer shorts: Shorts mainly used as male underwear. Some years ago, this term also related to a basic style male short.
 Track shorts: Shorts that reach only the upper thigh and are intended to give maximum freedom of movement in sports activities.
 Walking shorts: Shorts with a long pant length reaching to the knees. They are intended for casual wear in warm weather.  
 Cut-offs: Homemade shorts made by cutting the legs off trousers
 Hotpants: Commonly known as "short shorts" and are mostly worn by women. These are short, tight shorts. They are usually made out of cotton, nylon, or some other common material.  
 "Bun huggers": Short, tight, athletic shorts also known as "racing briefs". They are usually made from spandex and/or nylon. These shorts are commonly used for some adult athletic events such as volleyball.
 "Skorts": Shorts that have a piece of fabric in front so that from the front it looks like a skirt. It is a portmanteau of "skirt" and "shorts".
 "Zip-off shorts": A pair of long pants that zip off at the knee. They allow the wearer to change from pants to shorts as the weather changes.
 Board shorts: A combination of shorts and a bathing suit worn by men. They have recently gained in popularity. 
 Three quarter pants: A name used to refer to other types of shorts such as Shants or Shankles.
 "Capris": Shorts that reach below the knee.
 Baggies: Loose fitting shorts which reach the knees. 
 Cycling shorts: Special shorts designed for athletic use, originally in cycling.
 Bermuda shorts: A knee-length shorts commonly worn in Bermuda as business attire, or largely any style less than formal.
 Cargo shorts: Typically khaki shorts with cargo pockets, similar to cargo pants, except they are around knee-length.
 Boyshorts: Similar to boxer briefs, but for females.
 Jorts: Jean shorts using denim fabric.
 Lederhosen: Traditional German leather shorts.
 References