The three-dimensional arrangement of an
organic molecule that is caused by:
double bonds that prevent free rotation, or
chiral centers that have side groups arranged around them in a particular order.
A configurational
isomer can't be turned into another
configuration without breaking
covalent bonds.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.