Glossary Term Definition
A unit of typographic measurement equal to 12 points, approximately 4.22 mm in the Anglo-American system; used to measure line length, column width, and margins.
Definition
A unit of typographic measurement equal to 12 points, approximately 4.22 mm in the Anglo-American system. Picas are used to measure line length, column width, margins, and other horizontal and vertical page dimensions. The continental European equivalent is the cicero.
Source
No access — Robert Bringhurst — p. 328:
A unit of typographic measurement equal to 12 points.