ACRONYMS are abbreviations formed from the initial components in a phrase or name. These components may be individual letters (as in CEO) or parts of words. These are pronounced as a word either containing only Initial Letters (eg:NATO) or as names of letters (eg:FAQ) and many other ways
A backronym or bacronym is a phrase constructed purposely such that an acronym can be formed to a specific word. It is a blend of backward and acronym, and has been defined as a "reverse acronym".
IDIOMS & EXPRESSIONS
An idiom is a phrase where the words together have a meaning that is different from the dictionary definitions of the individual words. It is an expression, word, or phrase whose sense means something different from what the words literally imply.