BTN meaning in Softwares ?

In modern clothing and fashion design, a button is a small fastener, now most commonly made of plastic but also may be made of metal, wood, or seashell, that joins two pieces of fabric together. In archaeology, a button can be a significant artifact. In the applied arts and craft, a button can be an example of folk art, studio craft, or even a miniature work of art.

Buttons are most often attached to articles of clothing, but can also be used on containers such as wallets and bags. However, buttons may be sewn onto garments and similar items exclusively for purposes of ornamentation. Buttons serving as fasteners work by slipping through a fabric or thread loop or by sliding through a buttonhole. Other types of fastenings include zippers, Velcro, and magnets.