An IFR landing clearance is your authorization to land the aircraft. Unlike VFR, where you might simply be cleared for the circuit, an IFR landing clearance is specific: it clears you to descend below the minimum descent altitude and land on a specific runway. You must read back this clearance because it is a critical instruction.
The clearance takes several forms depending on the approach type and ATC workload:
"Runway [number], cleared to land" (simplest form)
"Runway [number] right hand circuit, cleared to land" (if turns are required)
"Runway [number], wind [direction and speed], cleared to land" (if wind information helps)