Heterozygous (Het): Having two different alleles of a particular gene in a gene pair. The two alleles may be different mutants or a wild type allele paired with a recessive mutant or a dominant mutant or a codominant mutant. For instance, a crossbreeding between an albino ball python and a normal ball python will produce offspring that have a normal gene paired with an albino (recessive) gene. These babies are heterozygous for albino. (See also homozygous, dominant, codominant, recessive.)

source: www.reptilekeepers.co.uk