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Expression \Ex*pres"sion\ ([e^]ks*pr[e^]sh"[u^]n), n. [L.
expressio: cf. F. expression.]
1. The act of expressing; the act of forcing out by pressure;
as, the expression of juices or oils; also, of extorting
or eliciting; as, a forcible expression of truth.

2. The act of declaring or signifying; declaration;
utterance; as, an expression of the public will.

With this tone of philosophy were mingled
expressions of sympathy. --Prescott.

3. Lively or vivid representation of meaning, sentiment, or
feeling, etc.; significant and impressive indication,
whether by language, appearance, or gesture; that manner
or style which gives life and suggestive force to ideas
and sentiments; as, he reads with expression; her
performance on the piano has expression.

The imitators of Shakespeare, fixing their attention
on his wonderful power of expression, have directed
their imitation to this. --M. Arnold.

4. That which is expressed by a countenance, a posture, a
work of art, etc.; look, as indicative of thought or
feeling. ``The expression of an eye.'' --Tennyson.

It still wore the majesty of expression so
conspicuous in his portraits by the inimitable
pencil of Titian. --Prescott.

5. A form of words in which an idea or sentiment is conveyed;
a mode of speech; a phrase; as, a common expression; an
odd expression.

6. (Math.) The representation of any quantity or relation by
appropriate characters or symbols, usually in a specific
order.
[1913 Webster +PJC]

7. (Genetics) the production of products by a gene that cause
the appearance of the corresponding protein or phenotype;
-- of a gene or of an organism with a specific gene; as,
the expression the beta-galactosidase positive phenotype,
[PJC]

8. (Computers) a combination of characters linked by
operators, occurring as part of the code of a computer
program, which must be evaluated according to the rules of
the computer language in order to produce a resulting
value.
[PJC]

Note: In most programming languages, (a + b) is an expression
indicating simple arithmetic addition, if the variables
a and b are real numbers. Many other types of operation
may be used in programs, and each set of symbols
indicating an operation is an expression in that
program.
[PJC]

{Past expression}, {Beyond expression}, beyond the power of
description. ``Beyond expression bright.'' --Milton.