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.