Distinctness describes the ease with which features can be identified. It is often used for mottle colour and surface coatings.
Faint:
Features can only be identified using 10x lens and cannot be positively identified in all places. They are generally thin and their contrast with the adjacent matrix is small.
Distinct:
Features have sufficient colour or texture contrast to be seen without magnification, but may need a lens for positive identification.
Prominent:
Features are conspicuous without magnification and can be readily distinguished from the matrix by sharp colour or texture contract or by their thickness. Some thin features, eg mangans can be prominent.