Coilovers are springs and struts together as a package (and they're usually both adjustable). Some adjustable springs are called coilovers as well, like Ground Control and SKunk2, but require aftermarket struts to control their high spring rates (otherwise you'll be in for a stiff, bouncy ride). Aftermarket off the shelf struts (KYB, Koni, Tokico, TRD
) are good for use with springs down to about a 1.5" drop. Any further and you'll either have to get custom struts made to handle the low drop, or replace your blown struts every year or two.