Spacing is the space around a glyph, defined by its side bearings (on the left and right side for a script written horizontally). Managing side bearings values is also referred as “managing the spacing.”
It controls the distance between glyphs and helps yo maintain a consistent rhythm and legibility once set in texts, making it an important aspect of a typeface’s quality.

Spacing can be adjusted manually, or with the help of coding scripts. Glyphs with similar shapes are often grouped into groups so their side bearings can be adjusted collectively: for example, o, d, c, e, q can often share the same left side bearing group. This ensures consistency and speeds up the spacing process across a typeface.

FONT ENGINEERING HINT

Side bearing values are stored in the hmtx (Horizontal Metrics) table for scripts written horizontally, and in vmtx (Vertical Metrics) for scripts written vertically.