A blouse most commonly refers to a woman's shirt, although the term is also used for some men's military uniform shirts.
South Asia
In India and South Asia, the traditional ladies' attire consists of two pieces of dresses called sari (somtimes also saree) and blouse. While the blouse is used to cover the breasts, the sari is draped around covering the whole body including the blouse, in a particular fashion. Sari and blouse remains the most popular garment for Indian women.
Western World
Blouses were rarely part of the fashionable woman's wardrobe until the 1890's. Before that time, they were occasionally popular for informal wear in styles that echoed peasant or traditional clothing, such as the Garibaldi shirt of the 1860's.
During the later Victorian period, blouses became common for informal, practical wear. A simple blouse with a plain skirt was the standard dress for the newly expanded female (non-domestic) workforce of the 1890's, especially for those employed in office work. In the 1900's and 1910's, elaborate blouses, such as the "lingerie blouse" (so-called because they were heavily decorated with lace and embroidery in a style formerly restricted to underwear) and the "Gibson Girl blouse" with tucks and pleating, became immensely popular for daywear and even some informal evening wear. Since then, blouses have remained a wardrobe staple.
Blouses are often made of cotton or silk cloth and may or may not include a collar and sleeves. They are generally more tailored than simple knit tops, and may contain "feminine" details such as ruffles or embroidered decorations.
Blouses have buttons reversed from that of a men's shirts. That is, the buttons are normally on the wearer's left-hand and the buttonholes are on the right. The reasons for this are unclear, however. Some suggest this custom was introduced by launderers so they could distinguish between women's and men's shirts. Another theory purports that the tradition arose in the Middle Ages when one manner of manifesting wealth was by the number of buttons one wore. Female servants were in charge of buttoning their mistress's gowns (since the buttons were usually in the back). Tiring of attempting to button the buttons backwards, they started reversing the direction of the buttons.