Abbreviation – a shortened form of a written word or a phrase used in a text in place of the whole for economy of space and effort (Example: abbr – abbreviation)
Acronyms – abbreviated words which tend to be read as though they were ordinary English words and sound like English words. (Example: NATO – the North-Atlantic-treaty-organization).
Initial abbreviation (Initialisms, or Alphabetisms) – abbreviations with the alphabetical reading retained i.e. pronounced as a series of letters (Example: B.B.C. – the British broadcasting corporation).