The title of a PatternLanguage in PatternLanguagesOfProgramDesign 2 by KentBeck and KenAuer.
The paper can be found in HTML form (not quite done as well as it could be) at http://www.rolemodelsoftware.com/moreAboutUs/publications/articles/lazyopt.php
The link seems to be broken... The archive to the rescue ... http://web.archive.org/web/20060703205625/http://www.rolemodelsoftware.com/moreAboutUs/publications/articles/lazyopt.php
Although the paper is called PatternsForEfficientSmalltalkProgramming, 90% of what they say is applicable to any language.
On this wiki, the pattern is more fully expounded in OptimizeLater and its AntiPattern in PrematureOptimization.