pro·gres·sion 
(prə-grĕshən)
(prə-grĕshən)n.
1. Movement or change from one member of a continuous series to the next: progression of the disease in stages.
2. A continuous series; a sequence: a progression of limousines. See Synonyms at series.
3. Mathematics A series of numbers or quantities in which there is always the same relation between each quantity and the one succeeding it.
4. Music
a. A succession of tones or chords.
b. A series of repetitions of a phrase, each in a new position on the scale.
pro·gression·al adj.