het means heterozygous for that particular trait

as in they carry it but it isn't physically expressed

AA = dominant (homozygous)
Aa= heterozygous
aa= recessive (homozygous)

the only way a het trait gets expressed is if the het animal is mated with a het or homozygous recessive animal....punnett squares 101 from genetics/gen bio

Aa x aa= Aa and aa (50% chance for either)

Aa X Aa= AA/Aa/aa 1:2:1 ratio (25%/50%/25%) chances