A 2-5-1 progression is a progression of chords that follow that series in the scale. For instance, in the key of C major a 2-5-1 progression would be these chords: D minor, G major, C major.
Also, these chords can be altered. For instance, you could have D7, G7 and C7, or some other alteration of these chords . . . but that is the progression.
In the key of Eb, a 2-5-1 progression would be F minor, Bb major, Eb major.
So it depends on the key in which you are in.
Be Blessed . . .