1. [n]  discourse that surrounds a language unit and helps to determine its interpretation
2. [n]  the set of facts or circumstances that surround a situation or event; "the historical context"

1. \Con*text"\, a. [L. contextus, p. p. of contexere to
   weave, to unite; con- + texere to weave. See {Text}.]
   Knit or woven together; close; firm. [Obs.]
         The coats, without, are context and callous. --Derham.
   

2. \Con"text\, n. [L. contextus; cf. F. contexte .]
   The part or parts of something written or printed, as of
   Scripture, which precede or follow a text or quoted sentence,
   or are so intimately associated with it as to throw light
   upon its meaning.
         According to all the light that the contexts afford.
                                                  --Sharp.
   

3. \Con*text"\, v. t.
   To knit or bind together; to unite closely. [Obs.] --Feltham.
         The whole world's frame, which is contexted only by
         commerce and contracts.                  --R. Junius.
   

That which surrounds, and gives meaning to, something else.

In a grammar it refers to the symbols before and after the symbol under consideration. If the syntax of a symbol is independent of its context, the grammar is said to be context-free.