Het means that a ball python is heterozygous for the morph in question. It means that the ball python has one Allele of the Gene for albino. There are two alleles in a gene, to have a albino ball python you need two for it to show albino. A het albino looks like a normal ball python but one of it's alleles in it's genes is albino, make sense? Read this article from Tim Cranwills page to understand how genetics work for snakes, very basic and easy to understand.
http://www3.mb.sympatico.ca/~cranwill/faq22.html
Mike