Ktav Ashuri in the context of "Hebrew"

The Hebrew alphabet (Hebrew: אָלֶף־בֵּית עִבְרִי, Alefbet ivri), known variously by scholars as the Ktav Ashuri, Jewish script, square script and block script, is a unicameral abjad script used in the writing of the Hebrew language. Alphabets based on the Hebrew script are used to write other Jewish languages, most notably Yiddish, Ladino, Judeo-Arabic, and Judeo-Persian. In modern Hebrew, vowels are increasingly introduced. Hebrew script is used informally in Israel to write Levantine Arabic, especially among Druze. The script is an offshoot of the Imperial Aramaic alphabet, which flourished during the Achaemenid Empire, and which itself derives from the Phoenician alphabet.

Historically, a different abjad script was used to write Hebrew: the original, old Hebrew script, now known as the Paleo-Hebrew alphabet, has been largely preserved in a variant form as the Samaritan alphabet, and is still used by the Samaritans. The present Jewish script or square script, on the contrary, is a stylized form of the Aramaic alphabet and was technically known by Jewish sages as Ashurit (lit. 'Assyrian script'), since its origins were known to be from Assyria (Mesopotamia).

The ancient Aramaic alphabet was used to write the Aramaic languages spoken by ancient Aramean pre-Christian peoples throughout the Fertile Crescent. It was also adopted by other peoples as their own alphabet when empires and their subjects underwent linguistic Aramaization during a language shift for governing purposes — a precursor to Arabization centuries later — including among the Assyrians and Babylonians who permanently replaced their Akkadian language and its cuneiform script with Aramaic and its script, and among Jews, but not Samaritans, who adopted the Aramaic language as their vernacular and started using the Aramaic alphabet, which they call "Square Script", even for writing Hebrew, displacing the former Paleo-Hebrew alphabet. The modern Hebrew alphabet derives from the Aramaic alphabet, in contrast to the modern Samaritan alphabet, which derives from Paleo-Hebrew.

The letters in the Aramaic alphabet all represent consonants, some of which are also used as matres lectionis to indicate long vowels. Writing systems, like the Aramaic, that indicate consonants but do not indicate most vowels other than by means of matres lectionis or added diacritical signs, have been called abjads by Peter T. Daniels to distinguish them from alphabets such as the Greek alphabet, that represent vowels more systematically. The term was coined to avoid the notion that a writing system that represents sounds must be either a syllabary or an alphabet, which would imply that a system like Aramaic must be either a syllabary, as argued by Ignace Gelb, or an incomplete or deficient alphabet, as most other writers had said before Daniels. Daniels put forward that this is a different type of writing system, intermediate between syllabaries and 'full' alphabets.