For the correct use of the terms standard or regulation and recommendation, it is necessary to take a look at the respective definitions, even if they are not always clear.
A standard is a universally legally recognized, generally valid and published rule for solving a problem, which has been approved by a standardization procedure. In the case of the term standard, which is also frequently used in the literature, a distinction must be made between its incorrect use as a synonym for the word standard and its meanings as an industrial standard and a manufacturer-specific standard. The former means that this set of rules has gone through the stages of a standardization procedure - at national or international level - and has subsequently been approved and published as a regulation.
Industry standard means that over the years, through the practice of many users and various manufacturers, it has proven technically useful and correct to adhere to a certain pragmatic set of rules for a certain problem, without an (inter)national standardization procedure having been carried out. A de facto standard may have originated from an industry standard. There are many examples where a de facto standard has emerged from an industry standard: The Disc Operating System( DO) is probably one of the best known de facto standards that has emerged from an industry standard. The compact cassette( CC), compact disc( CD), and Blu-ray disc( BD) are others. The best-known transport protocol, the TCP protocol, is also a de facto standard, as are many file formats or audio and RF connectors.
A manufacturer-specific standard, on the other hand, is even weaker: based on several years of experience, a large number of users have come to the conclusion that it is advantageous to follow a manufacturer's company-specific specifications.
Furthermore, the term recommendation can be found in the literature. This is the weakest form of standardization: users and manufacturers are not obliged to follow it in any case.