A contraction is a type of shortened phrase formed by substituting intermediate letters [and their sounds] for an apostrophe and merging the words together.
Examples of contractions:
- have not → haven't [the letter o is omitted and the words are effectively merged]
- I am → I'm [the letter a is omitted and the words are effectively merged]
Contractions are used to make communication more efficient, in both written and spoken language; the elision [the omission of one or more sounds in a statement] that occurs when letters are omitted serves to make spoken statements both easier to say and more concise for the listener.
They are not to be confused with abbreviations. Though not considered colloquial, the use of contractions is considered somewhat informal.