noun

• The result of shortening or reducing; abridgment.
• (linguistics) A shortened or contracted form of a word or phrase, used to represent the whole, utilizing omission of letters, and sometimes substitution of letters, or duplication of initial letters to signify plurality, including signs such as +, =, @.
• The process of abbreviating.
• (music) A notation used in music score to denote a direction, as pp or mf.
• (music) One or more dashes through the stem of a note, dividing it respectively into quavers, semiquavers, demisemiquavers, or hemidemisemiquavers.
• Any convenient short form used as a substitution for an understood or inferred whole.
• (biology) Loss during evolution of the final stages of the ancestral ontogenetic pattern.
• (mathematics) Reduction to lower terms, as a fraction.