What's a Polo ?
A polo shirt is a form of shirt with a collar, a placket neckline with three buttons, and an optional pocket. Polo shirts are usually short sleeved; they were originally used by polo players during the 1920s.
Polo shirts are usually made of knitted cotton (rather than woven cloth), usually a Piqué knit, or less commonly an interlock knit (the latter used frequently, though not exclusively, with pima cotton polos), or using other fibers such as silk, merino wool, synthetic fibers, or blends of natural and synthetic fibers. A dress-length version of the shirt is called a polo dress.
At the end of the 19th century, outdoor activities became important for the British ruling class. Jodhpur pants and polo shirts became part of the wardrobe for horse-related sports. The two garments were brought back from India by the British, along with the game of polo. The original polo shirts were more like contemporary button down sport shirts. They were buttoned, long- or short-sleeved shirts, distinguished by being made of more rugged material than dress shirts and featuring button-down collars to prevent the collars from flapping around when riding on horseback. For this reason, Brooks Brothers markets its line of oxford cloth button down shirts as "Original Polo."
In the 19th and early 20th centuries, tennis players ordinarily wore "tennis whites" consisting of long-sleeved white button-up shirts (worn with the sleeves rolled up), flannel trousers, and ties.This attire presented problems for ease of play and comfort.
Source : Polo Wikipedia