Clipping can be defined as a type of word formation, consisting in the shortening of a word to form a new one with the same meaning. The syllable or syllables removed can be at the end of a word: ad for advertisement, at the beginning: paper for newspaper, or at both the beginning and the end: flu for influenza, etc.
Sometimes slight modifications occur: fridge for refrigerator, mike for microphone, telly for television, etc.
Clippings generally have a restricted colloquial use: prof for professor, doc for doctor, veg for vegetables, etc., but in some cases, the clipped form has largely displaced the original; thus practically nobody nowadays uses perambulator, public house or omnibus any more, but their respective clipped forms: pram, pub and bus.
For other examples of clipping, see my book Short Stories to Help You Increase Your Vocabulary, Verticebooks, pp. 258-259.