Acronyms are terms created by using the initial letters of the several component words composing the name of an organization, program, or concept, to create a new word that substitutes for the combination of the component words. Initialisms are terms created by using the initial letters of several component words composing the name of an organization, program, or concept, to create a new term that substitutes for the combination of the component words.
Abbreviations are terms created by shortening larger terms.