Heterosomes are the sex chromosomes, i.e.: the 23rd pair of chromosomes in a karyotype. In a human female these are XX, and in a human male they are XY.
Humans have 1 pair of heterosomes, also known as sex chromosomes. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).
An autosome is a non-sex chromosome. It is an ordinarily paired type of chromosome that is the same in both sexes of a species. For example, in humans, there are 22 pairs of autosomes. The X and Y chromosomes are not autosomal. Non-autosomal chromosomes are usually referred to as sex chromosomes, allosomes or heterosomes.