A property of semivariogram models. Any linear combination of admissible models with positive coefficients can be nested or added together. Generally, single models are used for modeling experimental semivariograms that are close in shape to one of the basic admissible models, or for the approximate fitting of complex structural functions. Nested models are used to better fit complex structural functions.

Reference:

Olea RA: "Fundamentals of Semivariogram Estimation, Modeling, and Usage," in Yarus JM and Chambers RL (eds): 鈥淪tochastic Modeling and Geostatistics,鈥?AAPG Computer Applications in Geology, no. 3. AAPG, Tulsa, Oklahoma, USA, 1994.