An addition to chromaticblue's entry:

Blues scales: It's all to do with relative minors of the major scale
Note that numbers represent the degree of the scale (e.g. 1=C , 2=D in the scale of C) and 'b' means 'flatened'. So:
  • Minor blues: C, Eb, F, Gb, G, Bb, C
  • Major blues: C, D, Eb, E, G, A, C
(Although when improvising over a blueschord progression you could use both.)

The minor pentatonicscale also goes by the same rule and has a flattened third note
  • Major: 1, 2, 3, 5, 6, 8 (e.g. C, D, E, G, A, C)
  • Minor: 1, 2, b3, 5, 6, 8 (e.g. C, D, Eb, G, A, C)