If you're referring to One Engine Inoperative (OEI) performance, and I assume that you are :-
Gross Ceiling is the maximum Altitude / Level that may be maintained OEI with the remaining engine/s at MCT, and the aircraft flown at recommended Drift-Down speed. The Climb Gradient is (obviously) 0%.
Net Ceiling is the maximum Altitude / Level that may be achieved OEI with the remaining engine/s at MCT, and the aircraft flown at scheduled Drift-Down speed where the Climb Gradient is 1.1% (2 engined aircraft). Similar rules apply for the OEI en-route Climb.
In short, the 1.1% Delta between Gross and Net is the performance degradation OEI that we are accustomed to in other areas such as 2nd Segment Climb (in this case 0.8% for a 2 engined aircraft), or the artificial lengthening of the 3rd Segment.
The practical application of the 2 ceilings are that Gross Ceiling may be used for Flight Planning purposes, TAS, Fuel Flow etc. Net Ceiling is used to ascertain en-route Terrain clearance for the OEI "escape routes" en-route, or, where the original route may be maintained, that Net Ceiling equals or exceeds MEA. In level flight at the Net Ceiling, the 'normal' 1000 ft terrain clearance applies, but this is increased to 2000 ft during Drift-Down.