Shortenings (or contracted/curtailed words) are produced in two different ways. The first is to make a new word from a syllable (rarer, two) of the original word. The latter may lose its beginning (as in phone made from telephone, fence from defence), its ending (as in hols from holidays, vac from vacation, props from properties, ad from advertisement) or both the beginning and ending (as in flu from influenza, fridge from refrigerator).
The second way of shortening is to make a new word from the initial letters of a word group: U.N.O. ['ju:neu] from the United Nations Organisation, B.B.C. from the British Broadcasting Corporation, M.P. from Member of Parliament. This type is called initial shortenings. They are found not only among formal words, such as the ones above, but also among colloquialisms and slang. So, g. f. is a shortened word made from the compound girl-friend.
Here are some more examples of informal shortenings. Movie (from moving-picture), gent (from gentleman), specs (from spectacles), circs (from circumstances, e. g. under the circs), I. O. Y. (a written acknowledgement of debt, made from I owe you), lib (from liberty, as in May I take the lib of saying something to you?), cert (from certainty, as in This enterprise is a cert if you have a bit of capital), metrop (from metropoly, e. g. Paris is a gay metrop), exhibish (from exhibition), posish (from position).
