A site on the chromosome of the bacteria E. coli where the lambda bacteriophage can insert its genome (all of its DNA) so that it can lie dormant and have its DNA reproduced whenever the bacterium reproduces for as long as the bacterium remains healthy (that is, so that it becomes lysogenic).
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.