A satellite in some chromosomes is a small segment of a chromosome that is separated from the remaining part of the chromosome by a secondary constriction.
In humans, the satellite is seen as associated with a short arm of acrocentric chromosomes such as in chromosomes 13,14,15, and 21.
Secondary constriction :
The narrow regions are present on a chromosome other than the centromere (primary constriction).
This region is the site for the nucleolar organizer region that contains multiple copies of ribosomal genes which are required to synthesize RNA required by the ribosome.