What rear Axis shock?

[Axis400exRider]

I have dual rate fully adjustable Axis shocks up front, i want to get a dual rate fully adjustable shock in the back but wherever i look it says progressive after it. What does that mean??? Is it just a normal axis shock or what??

[devildriver422]

its one shock that they wind up tighter towards the top so that as it compresses it gets harder...does the same thing as a dual rate or triple rate...but with only one spring

[Axis400exRider]

Well what shock would you suggest for me to get in the back??