noun The first letter of the Proto-Canaanite alphabet, and its descendants in descended Semitic scripts, such as Phoenician 𐤀 (ʾ, ʾaleph), Aramaic 𐡀 (ʾ), Classical Syriac ܐ ('ālaph), Hebrew א (aleph) and Arabic ا (ʾalif).
noun The cardinality of an infinite well-ordered (or well-orderable) set.
The axiom of choice is equivalent to the proposition that every infinite cardinal is an aleph.