Verbal contraction
A verbal contraction was a shortened form of a word such as "can't" for "can not" or "isn't" for "is not". In slang, it was common to use improper contractions such as "ain't" instead of "isn't". ()

Lore was adept at using contractions, which he pointed out to Data in 2364, who did not have this ability. ()

Created in 2366, Lal's neural nets were based on Data's, but as she developed, she gained the ability to use verbal contractions. () 

By 2367, Data still could not use contractions, which (among other things) made William T. Riker realize he was not in the year 2383, but instead in a simulation created by Barash. () Later, Data would make two contractions ("I'm" and "can't"), but when Riker asks what he said, Data retracts by saying "cannot." However, Riker states that Data said "can't" and therefore used a contraction. 

Q occasionally used contractions in regular speech, but as part of his chaotic god title, this was not too often.  However, this was never pointed out in the series, unlike Data.

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Linguistics