A font scheme is a defined set of fonts that is associated with a publication. For example, a font scheme might be made up of one font for headings, one for body text, and another for captions. Font schemes make it easy to change all the fonts in a publication to give it a new look.
Within each font scheme both a major font and a minor font are specified. Generally, a major font is used for titles and headings, and a minor font is used for body text.