I think you do need to know a lot of style in Grade 5 but you do in Grade 6 and above.
Imitative is baroque period. (eg. the right hand plays a melody and then the left hand follows the same meolody after that)
Fugal...ummmmm let me check the dictionary.
Lyrical is like singing. Mostly in the romantic period. The melody is played loadly like someone singing.
Period:
Baroque-style=polyphonic(many molodies), imitative.[it is usually played on the harpsichord so the notes might be a bit detached)
Classical-style=homophony(1 melody), alberti bass
Romantic-style=homophony, expressive, pedalling
20th century-style=no tonal centre(many chromatic notes and absolutely tuneless) OR jazz like
I only have difficulty with baroque and classical.