Adverse Possession.
A portion of butter is called a Pat of butter
The upper portion of a fraction is called the numerator.
Portion of the area of a circle is called a sector.
The star studded portion of the American flag is called the Star Studded Portion.
The visible portion of the tooth is called the crown. The submerged portion is called the root.
A portion of a whole is a fraction of it.
the hull
The rear portion of a car is called the Hind Quarters.
the above portion of the earth is called the earth's crust
the spoon shaped portion of the scapula is called the olecranon process
The outer portion of the shadow is called the "penumbra".
The main portion or shaft of a long bone is called the diaphysis.