Whereas an abbreviation may be any type of shortened form, such as words with the middle omitted (for example, "Rd" for "Road" or "Dr" for "Doctor") or the end truncated (as in "Prof." for "Professor"), an acronym – in the broad sense – is formed from the first letter or first few letters of each important word in a phrase (such as "AIDS" from "acquired immuno-deficiency syndrome", and "scuba" from "self-contained underwater breathing apparatus"). However, this is a loose rule-of-thumb definition, as some acronyms are built in part from the first letters of word components (morphemes), as in the "i" and "d" in "immuno-deficiency", or using a letter from the middle or end of a word, or from only a few key words in a long phrase or name, as illustrated in some examples below. Less significant words like "in", "of", and "the" are usually dropped ("NYT" for "The New York Times", "DMV" for "Department of Motor Vehicles"), but not always ("TICA" for "The International Cat Association", "DoJ" for "Department of Justice").