(such as AIDS, from acquired immuno-deficiency syndrome, and scuba from self-contained underwater breathing apparatus). However, this is only a loose rule of thumb, as some acronyms are built in part from the first letters of morphemes (word components; 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. Less significant words such as 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). Abbreviations formed from a string of initials and usually pronounced as individual letters (as in FBI from Federal Bureau of Investigation, and e.g. from Latin ) are sometimes more specifically called initialisms or alphabetisms. Occasionally, some letter other than the first is chosen, most often when the pronunciation of the name of the letter coincides with the pronunciation of the beginning of the word (example: BX from base exchange). Acronyms that are usually pronounced as words, such as AIDS and scuba, are sometimes called word acronyms, to disambiguate them more clearly from initialisms, especially since some users of the term "initialism" use "acronym" in a narrow sense meaning only the type sounded out as letters. Another sub-type of acronym (or a related form, depending upon one's definitions) is the syllabic abbreviation, which is composed specifically of multi-letter syllabic (even multi-syllabic) fragments of the abbreviated words; some examples are FOREX from foreign exchange, and Interpol from international + police, though its full proper name in English is the International Criminal Police Organization. Usually the first syllable (or two) is used from each major component word, but there are exceptions, such as the US Navy term DESRON or DesRon from destroyer squadron. There is no special term for abbreviations whose pronunciation involves the combination of letter names with words, or with word-like pronunciations of strings of letters, such as JPEG () and MS-DOS (). Similarly, there is no unique name for those that are a mixture of syllabic abbreviations and initialisms; these are usually pronounced as words (e.g., radar from radio detection and ranging, consisting of one syllabic abbreviation and three single letters, and sonar from sound navigation ranging, consisting of two syllabic abbreviations followed by a single acronymic letter for ranging); these