Legal language is a phenomenon that can be approached from different perspectives. Over time, scholars have likened this feature for example to varieties of language, genres, registers or discourses. Some suggest that it covers not only the language of law itself (statutes and precedents), but also the language of legal doctrine and practice, possibly even legal jargon. Despite these comprehensive approaches to legal language, jurisprudence focuses only on certain types of legal communication and completely neglects others (this can be seen especially when contrasting the attention paid to written versus spoken speech). The key to preventing incompleteness in further research is to clearly define the content (intension) and scope (extension) of the concept. The first step then is to reach the intension of the concept and determine what criteria determine this ‘legal’ nature of language. The results of the analysis show that these determinants cannot be considered to be one particular form or the lexis used, but primarily the extra-linguistic circumstances within which a particular communication takes place, namely the roles of the participants, its context and its functions. Based on this definition, the extension of the concept under examination is constructed, i.e., a list of acts that should comprise legal language (based on the example of the Czech legal language). This list can provide a methodological basis for subsequent research with respect to the identified definition of legal language.