As happens with many concepts that regulate our rules, the profession concept is another whose knowledge and delimitation are taken of granted, as in our fundamental law as in the local rules that regulate it. However, this ambiguity brings asymmetries and disadvantages coming from the discretionary and laxity of their interpretation, generating disputes and unnecessarily costs. This article focuses on its clarification in light of others, as occupation and trade, with a brief historical review, and its entails with concepts derivative from: professional and being professional, with reference to legal texts: current Constitution and its predecessors, Constitutions of the States of the Republic, as well as the State laws, concluding with a proposed definition based on their essential elements. [ABSTRACT FROM AUTHOR]