The total interval of geologic time which is not represented by strata at a specified position along a given stratigraphic surface. If the hiatus encompasses a measurable interval of geologic time, the stratigraphic surface is an unconformity (Mitchum, 1977).

References
Mitchum Jr., R. M., (1977), Seismic Stratigraphy and Global Changes of Sea Level: Part 11. Glossary of Terms used in Seismic Stratigraphy: Section 2. Application of Seismic Reflection Configuration to Stratigraphic Interpretation, Memoir 26 Pages 205 - 212. )