A glyph is the graphic shape of a character in a writing system. The distinction between the abstract concept of a character and the concrete one of the glyph is a central distinction in the Unicode Standard (ch. 2, pp. 11–12). It is also a useful term in paleaography, even if this discipline prefers a term like letter-form. A character can be instantiated in a number of glyphs, which can sometimes look surprisingly different. This observation applies to the variation between fonts (or indeed hand-writings), but sometimes also to the distinction between regular and italic shapes.
See the entry on character for an illustration of various glyphs.
Reference
– The Unicode Standard. Version 8.0. Edited by Julie D. Allen et al. Unicode Consortium, Mountain View, CA. http://unicode.org/versions/Unicode8.0.0
In other languages
DE: Glyphe (f.)
FR: glyphe (f.)
IT: glifo (m.)