The word heterozygous is used to describe a person who inherited two different alleles for a particular trait.
Many genes have two or more differing forms (such as eye color or hair texture) which are called alleles. When a person inherits two different alleles for a trait they are said to be heterozygous for the trait (with hetero meaning other or different). When a person is heterozygous for a trait whichever allele is dominant will be expressed. So if someone inherited a heterozygous allele for hair color (Br) with 'B' denoting a dominant allele for brown hair and 'r' denoting a recessive allele for red hair, the dominant trait of brown hair would be expressed.