A small, fringed, four-cornered garment worn throughout the day (and sometimes night) by Jewish males.
The tallit katan ("small tallit") is a fringed garment traditionally worn either under or over one’s clothing by Jewish males. It is a poncho-like garment with a hole for the head and special twined and knotted fringes known as tzitzit attached to its four corners. The requirements regarding the fabric and fringes of a tallit katan are the same as that of a tallit gadol. Generally a tallit katan is made of wool or cotton.
While all four cornered garments are required to have tzitzit, the custom of specially wearing a tallit katan is based on a verse in Numbers 15:38-39 which exhorts Jews to "remember[ance of] all the commandments of the Lord." Wearing a tallit kattan is not mandated in Biblical law, but in Rabbinic law the practice is strongly encouraged for men, and often considered obligatory or a binding custom.
The tallit katan is also known as arba kanfot (Yiddish/Ashkenazic Hebrew: arba kanfos), literally "four corners" or tzitzit.