Sentence:  The concept of <WSD>convex envelopes</WSD> of nonconvex functions is a basic tool in theory and algorithms of global optimization, see e.g., Falk and Hoffman (1976), Horst and Tuy (1996), Horst et al. (2000). 
Meaning of the word marked with <WSD> tags:  For a given set S\subseteq\mathbb{R}^n and real-valued function "f" defined on the convex hull conv("S"), the highest-valued convex function that underestimates or equals "f" over "S".