A riff is a repeated chord progression or melodic figure, often played by the bass instruments, that forms the basis or an important part of a rock music or jazz composition; an ostinato figure.
Examples of music that depend on riffs for their effect:
... C. Pinckney[?]
14
Federalist
Rufus King (14)
Other elections: 1792, 1796, 1800, 1804, 1808, 1812, 1816
Source: U.S. Office of the Federal Register ...