Special languages and languages for special purposes

In all studies of a more or less recent nature in specialized languages and the teaching of foreign languages in specific contexts, there is a spread of terms that seem to belong to the same conceptual field: language (s) in the specialty, special language (s), specialized language (s), language (s) for special purposes, etc. Are all these names variants of the same term or denote different ideas and realities? Thus, the main purpose of this work is to try to establish several terminology clarifications concerning certain concepts of this set of terms and the application of their specificity for educational purposes, especially about the conceptual distinction between special languages and languages for special purposes.