Grade/class:

Peaks are assigned two difficulty ratings (Class and Grade). It is assumed that climbers use the least difficult, but not necessarily the most commonly-used, route accessible by automobile (not a 4 wheel drive vehicle). Driving time is not a factor.
A class of 1 to 6 is assigned to convey what type of terrain may be encountered. Briefly,
*  Class 1 is hands-in-pockets hiking;
*  Class 2 is rough cross-country travel;
*  Class 3 is simple climbing with some exposure; and
*  Class 4, 5, and 6 represent increasingly difficult climbing requiring the use of ropes and special equipment.
A class prefaced by an “S” is sometimes added to convey a greater degree of difficulty in climbing a summit block.
Grades are assigned as follows:
1) up to 5 miles round trip,
2) 6-10 miles round trip,
3) 11 to 15 miles round trip, etc.
and
A) up to 1,000′ total elevation gain,
B) 1000′ to 2000′ total elevation gain,
C) 2000′ to 3000′ total elevation gain, etc.
For example, a 21-mile jaunt climbing a total of 3500 feet is graded 5D.

Emblem class:  Star/Emblem/Mountaineer:

The peaks are classified as Star (*), Emblem (x), and Mountaineer (o) peaks according to their view, difficulty, and dominance of an area. Star peaks are primary in setting with exceptional views and are generally of greater difficulty.  Emblem peaks are secondary. Mountaineer peaks comprise the remainder. All provide a rewarding experience.

Prominence:

In topography, prominence characterizes the height of a mountain or hill’s summit by the vertical distance between it and the lowest contour line encircling it but containing no higher summit within it.   It is a measure of the independence of a summit.