What does font weight refer to?

Font weight specifically pertains to the thickness of the lines that compose the characters in a typed text. It denotes how bold or light the characters appear when rendered. Different font weights can convey hierarchy or emphasis in text; for instance, using a bold font weight can make certain text stand out more than regular or light variations.

While style variations of typefaces, spacing between characters, and font size are important aspects of typography as well, they are not synonymous with font weight. Style variations deal more with the design differences within a typeface family, such as italic or condensed forms. Spacing between characters relates to tracking and kerning, affecting how close or far apart letters are positioned. The size of the font is simply a measurement of how large or small the text appears, which also does not pertain directly to weight. Thus, the definition of font weight being the thickness of font lines is indeed accurate and relevant in the context of typography.