ThreeLine

Threeline is a term used in various contexts to refer to anything featuring three lines or a design motif of three lines. It is not a single, universally defined concept, but a label applied in design, mathematics, and branding.

In design and branding, threeline denotes a motif of three parallel lines. This minimalist element appears in logos, signage, and user interfaces, where it conveys simplicity, order, and rhythm. A familiar related symbol in digital interfaces is the three-line “hamburger” menu, used to indicate a collapsible navigation panel; while not always officially called threeline, the association with three lines is widespread and recognizable.

In mathematics, the three-line lemma is a standard result about exact sequences in a commutative diagram. It concerns the relationships among three parallel rows and their connecting maps, and it provides conditions under which the exactness of the middle row follows from the outer rows. The term is common in textbooks and lectures, though formal references frequently use the name “three-line lemma” or sometimes “ladder lemma.”

In other domains, threeline can appear as a brand name, product line, or project title. Because it is not tied to a single canonical subject, the meaning of threeline depends heavily on context, and readers should seek clarifying information when the term appears. See also: hamburger menu, triple, line, ladder lemma.