In English, the word is used in two ways. In the narrow sense, an acronym is a sequence of letters (representing the initial letters of words in a phrase) when pronounced together as a single word, like NASA, NATO, or laser. In the broad sense, the term includes this kind of sequence when pronounced letter by letter (such as GDP or USA). Sources that differentiate the two often call the former acronyms and the latter initialisms[1][2][3] or alphabetisms. However, acronym is popularly used to refer to either concept,[4] and both senses of the term are attributed as far back as the 1940s.[5]
https://en.wikipedia.org/wiki/Acronym