Abstract
The article discusses the various approaches to the concept of external definability developed in ominimal theories.An example of o-minimal theories shows how external constants help determine the existence of a solution in a model of a formula with external constants.The basic concepts are formulated with the help of which external definability is proved.A brief review of the results for dependent theories is given.In conclusion, sufficient conditions are formulated so that the NSOP theory has the some property of external definability.A brief explanation of the stated theorem is given.Keywords: externally definable, neighborhood of tuple of the set in the type, non orthogonality of two types.