An acronym is an abbreviation coined from the initial letter of each successive word in a term or phrase (compare initialism). For example, NATO for the North Atlantic Treaty Organization. In most cases, acronyms are capitalized, but after long use the abbreviation becomes a word in its own right and is spelled with small letters, like SCUBA, Self Contained Underwater Breathing Apparatus (now scuba).
In general, an acronym made up of more than the first letter of the major words in the expanded form is rendered with only an initial capital letter (Comsat from Communications Satellite Corporation; an exception would be NAM from Nonaligned Movement).
Hybrid forms are sometimes used to distinguish between initially identical terms (ICC for International Chamber of Commerce and ICCt for International Criminal Court).