FFP= First Focal Plane = The reticle stays the same subtension no mater what power it is on. In low power the reticle is smaller in high power the reticle is bigger. Takes a little getting used to until you realize you can hold, lead and measure stuff with it.
SFP= Second focal plane = The reticle stays the same size but the picture grows and shrinks around it. Only usefull for holds, leads and measuring on one power. Normally near the the highest power.
Cheers,
Craig6