Iōta (ἰῶτα) is the Greek name for the tenth letter of the Greek alphabet, and in the NT context of Matthew 5:18, the equivalent of the Hebrew yod (י) — the smallest letter in the Hebrew alphabet. Jesus uses it as the image of the very least, the smallest detail of Scripture, declaring that not even an iota will pass from the Law until all is fulfilled.
Matthew 5:18 — "Truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished\” — is Jesus' most emphatic statement about the indestructible authority and total fulfillment of Scripture. The iota (yod) is so small it barely changes word forms, and the "dot" (keraia) refers to the tiny calligraphic serif that distinguishes one Hebrew letter from another. Even these infinitesimal elements of Scripture are permanent and consequential.
This statement has massive implications: (1) Scripture is verbally inspired to the letter. (2) Every law and prophecy will be fulfilled — not spiritualized away. (3) Jesus did not come to abolish but to fulfill — His obedience was iota-complete. The theological weight of the smallest letter of the alphabet in Jesus' teaching makes it one of the most significant single nouns in the NT.