A jot is the smallest letter or written mark, used figuratively for something extremely small. The term represents Greek iota and may also correspond to Hebrew yod, the smallest Hebrew letter. In the written Law, it signifies even the least letter or part of a letter.
Jesus declared that not even a jot or the smallest part of a letter would pass from the Law until all was fulfilled. The saying emphasizes the enduring completeness of the written Law.
The reference concerns Hebrew synagogue rolls. The supplied material distinguishes the jot from the tittle, which is the smallest part of a letter.