This is an intermediate molecule involved in the fourth step of glycolysis. Dihydroxyacetone phosphate is created from fructose 1,6-bisphosphate. In step 5, it is converted into its positional isomer, glyceraldehyde 3-phosphate, with the aid of triose phosphate isomerase.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.