Most everyone knows what a major scale sounds like -- if you play all the white keys on the piano from C up to the next C an octave higher, that is the C major scale. You played all the white keys, but left out all the black keys. You played 8 white keys -- from the lowest C up to the highest C -- and you played a combination of whole steps (when you skipped a black key) and half steps (like between E and F, and B and C).
Now instead of leaving out the black keys, play ALL the keys from C to C -- black and white. Instead of an 8 note scale, you have a 13 note scale, and that is called a CHROMATIC SCALE. You could have started at any point -- not just on C -- and it would still be a chromatic scale. So a chromatic scale is entirely made up of half steps -- no whole steps -- you play every key, black and white.
A chromatic progression, therefore, is a chord progression that moves up of down by 1/2 steps; for example, from the C chord to the Db chord, or the F# chord to the G chord, and so on.