Extrapolation is a methodology that involves making statistical forecasts using historical trends projected for a specified period of time into the future. This is a type of estimation of the value of a variable based on its relationship with another variable. In that sense, it resembles interpolation, which does produce estimates between known observations; however, extrapolation is subject to higher uncertainty and a higher risk of producing meaningless results.
Extrapolation can also mean the extension of a method, assuming that similar processes are applicable. It can apply to human experience to project, extend or expand the known experience into an unknown or previously experienced area to gain (usual conjecture) knowledge of the unknown. The extrapolation method can be applied to the problem of internal reconstruction.