The term sub-soil is used for horizon

The term sub-soil is used for the horizon is C.
The C horizon is below the solum horizons. This layer is little affected by pedogenesis. The C horizon forms either in deposits or formed from weathering of residual bedrock.
The C horizon may be enriched with carbonates carried below the solum by leaching. If there is no lithologic discontinuity between the solum and the C horizon and no underlying bedrock present, the C horizon resembles the parent material of the solum.