Used in place of "double-u double-u double-u" before the "dot com" of a website address in spoken conversation. Who has time to spell out that tongue twister anyway?

WWW; world wide web; only two syllables versus nine in "double-u-double-u-double-u"

an alternate way of phrasing the beginning of a Universal Resource Locator aka URL, web address beginning with "www." Instead of "doubleyou, doubleyou, doubleyou", tri-dub abbreviates the same thing.

Instead of saying WWW. (which is nine syables, ten with the dot) a person says tri-dub dot whatever.