The acronym "ISM" stands for "Industrial, Scientific and Medical", i.e. for radio frequency applications in industry, science and medicine. The ISM frequencies are internationally allocated for use by RF equipment. Examples are spark erosian machines, microwave ovens and radio frequency treatment in medicine.
Apart from these applications the ISM frequencies may also be used for message transfer. Due to the inevitable radiated disturbance caused by the actual ISM application, the ISM frequencies risk being interfered with in the case of applications close to RF equipment. But in the modern world of communications, frequencies are a valuable resource that should be used efficiently. It therefore seemed obvious to use the ISM frequencies for those applications in which transient interference would be acceptable and in which only short distances would have to be bridged. The basic concept was that radio devices on ISM frequencies should be freely usable by everyone, exempt from licensing and should not require separate frequency assignment. General assignments in the ISM bands for short-range radio were hence amongst the first general assignments to be issued.
As a rule the ISM frequencies are allocated to other services on a primary or secondary basis. Primary and secondary users may not experience any interference from ISM applications. Conversely, ISM users must accept interference caused by other radio services.