A digital font does more than associate each character with a fixed bitmap. Modern outline fonts describe scalable glyph geometry together with metrics and other rendering data.

A character is an abstract text element such as the letter A; a glyph is a particular visual shape used to render text. The relationship is not always one-to-one: shaping can select ligatures, contextual forms or script-specific glyphs.

Outline fonts store glyph contours using curve segments. TrueType outlines use quadratic Bézier segments, so the same geometric description can be scaled to many sizes before being rasterized onto a pixel grid.

At small sizes, mapping smooth outlines to coarse pixels can make nominally equal stems appear unequal, remove details or distort spacing. Hinting or grid fitting adjusts the scaled outline so important visual relationships survive rasterization more consistently.

OpenType/TrueType fonts are structured as tables containing mappings, outlines, metrics and optional instruction programs. This separates the reusable geometric representation from the device-specific act of rasterizing it.

The next unit examines how TrueType can encode executable hinting instructions rather than only declarative outline data.