A membrane-bound section at the tip of the head of a sperm which contains lytic enzymes (hyaluronidase in mammalian sperm) which break down the outer coat of the egg and allow the sperm to inject its haploid DNA. The acrosome is secreted by the Golgi apparatus of the spermatid (young sperm cell).

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.