Both acronyms and abbreviations are short forms of words. However, there are difference:
An abbreviation begins wtih the initial letter of the word and contains a group of alphabets from the word. For example, "govt" is the abbreviation for "government", "Mr." for "Mister".
An Acronym takes up initials of all words in the phrase or group of words to make it convenient for people. For example, "USA" is the acronym for "United States of America" or "United States Army", "NIH" for "National Institutes of Health"
Acronym expansions are potential multiwords. Acronym expansions identified from the MEDLINE n-gram set are used as multiword candidates for adding multiwords to Lexicon. Following patterns are used to retrieve acronym expansions.