With the topic of LIPs (week 7), sequences are useful discussion. There are 2 main types: melodic and harmonic.
A melodic sequence is a chunk of music or motive repeated, but most/all the notes transposed up or down a consistent interval. Sequences are often used in developmental or transitional passages, and can also be embellished and transformed in other ways.
A harmonic sequence (aka root progression) is a series of chords in which the roots of the chords move by a consistent interval. Tr-Pr-D-T is a root progression where each time the root falls by 5th. This is known as a falling fifths sequence. T-Tr-P-Pr is a sequence where all the roots fall by third – a falling third sequence. (Pachelbel’s cannon is the most famous example of this falling 3rds sequence.) Chords in harmonic sequences can be in root position, all inverted, or some inverted ( in a pattern or not). The important part is the root of the chord, not the bass pitch. Root progressions can also be embellished with interpolated applied dominants.
Melodic and harmonic sequences sometimes occur concurrently. Both can be diatonic or chromatic.