From The Free On-line Dictionary of Computing (27 SEP 03) :
abstraction
1. Generalisation; ignoring or hiding details to capture some
kind of commonality between different instances. Examples are
abstract data types (the representation details are hidden),
abstract syntax (the details of the concrete syntax are
ignored), abstract interpretation (details are ignored to
analyse specific properties).
2. Parameterisation, making something a function
of something else. Examples are lambda abstractions (making
a term into a function of some variable), higher-order
functions (parameters are functions), bracket abstraction
(making a term into a function of a variable).
Opposite of concretisation.
(1998-06-04)