\Pro*gres"sion\, n. [L. progressio: cf. F.
progression.]
1. The act of moving forward; a proceeding in a course;
   motion onward.
2. Course; passage; lapse or process of time.
         I hope, in a short progression, you will be wholly
         immerged in the delices and joys of religion.
                                               --Evelyn.
3. (Math.) Regular or proportional advance in increase or
   decrease of numbers; continued proportion, arithmetical,
   geometrical, or harmonic.
4. (Mus.) A regular succession of tones or chords; the
   movement of the parts in harmony; the order of the
   modulations in a piece from key to key.
{Arithmetical progression}, a progression in which the terms
   increase or decrease by equal differences, as the numbers
   [lbrace2]2, 4, 6, 8, 1010, 8, 6, 4, 2[rbrace2] by the
   difference 2.
{Geometrical progression}, a progression in which the terms
   increase or decrease by equal ratios, as the numbers
   [lbrace2]2, 4, 8, 16, 32, 6464, 32, 16, 8, 4, 2[rbrace2]
   by a continual multiplication or division by 2.
{Harmonic progression}, a progression in which the terms are
   the reciprocals of quantities in arithmetical progression,
   as 1/2, 1/4, 1/6, 1/8, 1/10.