A blouse most commonly refers to a woman's shirt, although the term is also used for some men's military uniform shirts.
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. Several theories exist although none have conclusive evidence. Some suggest this custom was introduced by launderers so they could distinguish between women's and men's shirts. One theory purports that the tradition arose in the Middle Ages when one manner of manifesting wealth was by the number of buttons one wore. Another that the original design was based on armour which was designed so that a right-handed opponent would not catch their weapon in the seam and tear through, this would also mean that a person could draw a weapon with their right-hand without catching it in a loose seam of their own clothes. Female servants were in charge of buttoning their mistress's gowns (since the buttons were usually in the back). They tired of attempting to deal with buttons that were, from their point of view, backwards and as such they started reversing the placement when making or repairing them.
Although in all the cases proposed the reasons for the distinction no longer exists it continues out of custom or tradition