The Tallit katan ("small tallit") is a fringed undergarment worn by Orthodox, Hasidic and some Conservative 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 tallit can be made of any materials except a mixture of wool and linen interwoven which is strictly prohibited by the Torah. Most traditional tallitot (plural of tallit) (tallesim in Ashkenazic Hebrew) are made of wool.
The custom of 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." [1]
The tallit katan is also known as arba kanfot (Yiddish/Ashkenazic Hebrew: arba kanfos), literally "four corners," or tzitzit.