This paper focuses on two of the major problems that have traditionally hindered the study of the so-called 'colloquial Spanish', namely (i) terminological hesitation and lack of consensus in referring to this linguistic form (designated indistinctly by terms such as 'language', 'speech', 'discourse', etc., on one side, and 'colloquial', 'spoken', 'conversational', etc., on the other side) and (ii) the lack of a clear and unitary definition of the object of study. For this purpose, first the most common designations and the conditions which make it possible to use them as synonymous are identified. Secondly, the conceptual structure of the most famous definitions and the linguistic and extralinguistic features of the object of study which each one of them emphasizes are analyzed. Finally, reasons for the perpetuation of the terminological and conceptual vagueness in the history of Spanish Linguistics are mentioned and a theoretical frame for a better definition of spoken or colloquial Spanish is suggested. [ABSTRACT FROM AUTHOR]