Acronyms, initialisms, and alphabetisms are abbreviations that are formed using the initial components in a phrase or name. These components may be individual letters (as in CEO) or parts of words (as in Benelux or Delmarva). There is no universal agreement on the precise definition of the various terms (see Nomenclature), nor on written usage (see Orthographic styling). While popular in recent English, such abbreviations have historical use in English, as well as other languages]]. As a type of word formation process, acronyms and initialisms are viewed as a subtype of blending.

Nomenclature

While the word abbreviation refers to any shortened form of a word or a phrase, some have used initialism or alphabetism to refer to an abbreviation formed simply from a string of initials. In 1943, Bell Laboratories coined the term acronym as the name for a word (such as SONAR) created from the first letters of each word in a series of words (such as SOund Navigation And Ranging). The terms initialism and alphabetism are neither widely used nor widely known. The term acronym is widely used to describe any abbreviation formed from initial letters.Merriam-Webster, Inc. Merriam-Webster's Dictionary of English Usage, 1994. ISBN 0-877-79132-5. pp. 21–2:

acronyms   A number of commentators (as Copperud 1970, Janis 1984, Howard 1984 and according to Apple Inc.) believe that acronyms can be differentiated from other abbreviations in being pronounceable as words. Dictionaries, however, do not make this distinction because writers in general do not:

"The powder metallurgy industry has officially adopted the acronym 'P/M Parts'" —Precision Metal Molding, January 1966.
"Users of the term acronym make no distinction between those which are pronounced as words ... and those which are pronounced as a series of characters" —Jean Praninskas, Trade Name Creation, 1968.
"It is not J.C.B.'s fault that its name, let alone its acronym, is not a household word among European scholars" —Times Literary Supp. 5 February 1970.
"... the confusion in the Pentagon about abbreviations and acronyms—words formed from the first letters of other words" —Bernard Weinraub., N.Y. Times, 11 December 1978.
"An acronym is a pronounceable word..." —Apple Publications Style Guide"

Pyles & Algeo 1970 divide acronyms into "initialisms," which consists of initial letters pronounced with the letter names, and "word acronyms," which are pronounced as words. Initialism, an older word than acronym, seems to be too little known to the general public to serve as the customary term standing in contrast with acronym in a narrow sense.