How do I define the differences between a perfect, plagal, imperfect and interrupted cadence?

A cadence is a chordal progression that ends a phrase or piece of music. Perfect and plagal cadences provide a harmonically stable end to the music, whereas the imperfect and interrupted cadences make the music sound unfinished or surprising. 

A perfect cadence uses the chordal progression V-I in the home key and is the most commonly used cadence in tonal music. A plagal cadence uses the chordal progression IV-I in the home key, and is an easy cadence to remember and distinguish against a perfect cadence as it is the 'Amen' chord. 

An imperfect cadence ends on the dominant, chord V, making the music sound 'unfinished'. Any chord may be used to predecess the dominant but most commonly the tonic will do so e.g. I-V. An easy way to remember the imperfect cadence is that it is the opposite to a perfect cadence. An interrupted cadence begins as a perfect cadnece with chord V, however finishes on a minor chord giving the impression of an 'interrupted' perfect cadence, which makes the music sound surprising. A common example of this cadence is the chordal progression from V-vi.