Maxam-Gilbert sequencing is a lab technique used to discover the sequence of nucleotide bases in a nucleic acid (a DNA or RNA molecule).
The technique involves putting copies of the nucleic acid into separate test tubes, each of which contains a chemical that will split the molecule at a different base (either adenine, guanine, cytosine, or thymine or uracil; the last depending on whether it is DNA or RNA). The result is that each of the test tubes contains fragments of the nucleic acid that all end at the same base, but at different points on the molecule where the base occurs.
The contents of the test tubes are then separated by size with gel electrophoresis (one gel well per test tube; four total wells); the smallest fragments will travel the farthest and the largest will travel the least far from the well. The sequence can then be determined from the picture of the finished gel by noting the sequence of the marks on the gel and from which well they came from.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.