Glossary Term Definition
The relative thickness of the strokes in a typeface, ranging from hairline to ultra-black.
Definition
Weight refers to the relative thickness or heaviness of the strokes that make up the letterforms in a typeface. It is one of the primary axes of variation in a type family, typically ranging from thin or hairline through light, regular, medium, semibold, bold, extrabold, and black (or ultra-black). Weight affects both the color of the text (the overall darkness of a block of type on the page) and its visual emphasis. Skillful use of weight creates hierarchy and contrast without changing the typeface itself. In variable font technology, weight is a continuous axis rather than a set of discrete steps.
Source
No access — Robert Bringhurst — p. 346:
The darkness of the letterforms, measured by the ratio of the stroke width to the height or width of the letter.