Dominance

A genetic term used when describing an allele whose phenotype is expressed in organisms both homozygous for that allele and heterozygous (it masks another allele - a recessive allele).  

There are three types of dominance:

Complete Dominance - recessive phenotypes are only present in homozygous recessive organisms

Incomplete Dominance - heterozygotes resemble neither the dominant nor the recessive phenotype

Co-dominance - heterozygotes are a mixture of both the dominant and recessive phenotypes