Verify the true performance of your design while reducing the impact of the signal path, probe, cables, fixtures and other accessories used to measure the signal.
Whether you are debugging a high-speed interface such as DDR or PCIe, characterizing a fast clock or analyzing a complex RF signal, you want to see the real signal and not artifacts of the test setup such as loading or reflections. The process of removing non-ideal signal path effects (attenuation, skew, loading, etc.) is called deembedding.