Glossary Term Definition
The angle of inclination of the main strokes in an italic or oblique typeface, measured from the vertical.
Definition
Slope refers to the angle of inclination of letterforms in italic or oblique type, measured in degrees from the vertical axis. Most Renaissance italics have a slope of around 7–10 degrees, while later designs may lean as far as 12–15 degrees. Slope is distinct from the axis of the letterform: a letter may have a humanist axis (tilted stress) in either an upright or sloped posture. Oblique types are mechanically slanted versions of roman forms; true italics are independently designed with a different stroke logic, though both exhibit slope.
Source
No access — Robert Bringhurst — p. 345:
The angle of inclination of the stems and extenders of letters. Most italics have a slope between 2° and 20°.