An abbreviation is a sequence of alphanumeric characters that you type to reach expansions.
Instant Text keeps track of the last abbreviation you type, in order to suggest potential expansions in the Word and Phrase Expansion Tables.
Note that there is a subtle distinction between abbreviations and Word Entry Short Forms or Phrase Entry Short Forms. In either case short forms define a complete scope of possible abbreviations to reach an expansion.
And don't get it wrong, long phrase entry short forms do not not imply longer abbreviations. They just enhance a larger scope of possible abbreviations.