Introduction: The article discusses the problems associated with the definition of legal concepts which have the feature of “open texture”. The introduction presents the nature and meaning of “open texture”, which is understood as a special kind of indeterminacy. Such concepts are considered in the form in which they were postulated in the works of the Austrian linguistic philosopher Friedrich Waismann and the British legal philosopher Herbert Hart.Theoretical Basis. Methods. It is contested that, in Hart's interpretation, “open texture” appears in legal concepts in borderline cases, when the meaning of the term of “concept” becomes indeterminate, unclear, uncertain, and we do not know whether or not it should be applied. Such cases should be distinguished from clear-cut cases where such doubt does not arise.The methodological basis of the study is Hart's thesis stating that legal concepts have “core” and “penumbra” of meaning. The “core” meaning indicates a set of certain conditions, in which the use of the