What is meant by the term SAT or satellite?

The chromosome region where it connected is known as the SAT or satellite region.

Nucleolus Structure:

The nucleolus is a relatively bright compact spherical body found in the nucleus. Protein, lipid, and RNA make up the structure. It was discovered by Fontana in 1781, and Bowman named it nucleolus in 1840. The fibrous, granular, and matrix portions of the nucleolus are normally separated. In a nucleus of a eukaryotic cell, there is usually just one nucleolus.

Nucleolus' function is to synthesize and conserve different forms of RNA and protein.