Amateur radio is a technical activity in which people communicate with and experiment with radio.
The ability to experiment with radio is an important distinction between amateur radio and other ways in which members of the public are allowed to use radio such as Citizens’ Band, Family Radio Service and Business Radio. Because radio amateurs are allowed to experiment with radio, they are required to pass tests or examinations to prove a level of technical competence before being granted a license. For other types of radio license no tests are required, but experimentation is not permitted and users may only use approved types of equipment with limited power and simple antennas in order that they do not unknowingly cause interference to other radio users.
The ability to experiment also provides an important justification for reserving valuable frequency bands for use by radio amateurs. In the United Kingdom, radio amateurs are granted a license for the purpose of training themselves in wireless communication. Amateur radio allows you to learn skills valuable for a career in engineering and provides the country with a pool of skilled radio operators for use in times of war.
Radio amateurs are permitted to build and modify the equipment and antennas that they use on the air. For many, that is the main interest. Others may do no building or experimenting at all. But because amateur radio equipment can operate on many different frequencies and amateurs are permitted to assemble their own stations using a variety of equipment and use high power, a considerable level of technical knowledge is still required.
The main distinction between amateur radio and other radio services is therefore that amateur radio is a hobby for people who are interested in radio. If you simply want to communicate using radio and have no interest in knowing how it works then CB, FRS or business radio will be more suitable for your needs.
An important distinction between amateur radio and business radio is that radio amateurs are not allowed to use amateur radio for communications of a commercial nature. So you could not use amateur radio to pass messages related to a business activity or play music even if everyone involved had passed the tests and obtained amateur radio licenses.