School me on hydraulic vs solid flat tappet cams

So I have an old Cam Dynamics cam that I want to use in my cheap 360 build. It was given to me. With it, I also was given grooved shafts and adjustable rockers and 12-14 solid lifters thrown in a box.

My question is this: What makes a cam a solid vs hydraulic lifter cam? Lobe ramp angle? Does it really matter?