(and more spefically, interval
lic) terms, an unequal fifth
is a perfect fifth
followed a diminished
fifth, or the reverse.
Unequal fifths have been the subject of no small amount of debate, but unequal fifths do not fall under the same restrictions that normal fifths do.
As a general rule, all unequal fifths in voice leading
are acceptable unless a diminished fifth resolves to a perfect fifth with these intervals occuring between the bass
and another voice.