Route descriptions:  Difference between Grade, Class and Mazama grade

Most climbers are familiar with the term class, to describe the difficulty of an individual move on a particular rock or scrambling route.  For example a “4th class scramble”, or a “5.3 alpine rock route”. 
However, “class” is often confused with “grade”, which describes the general time required to complete an alpine route.  (Then there’s that wacky “Mazama grade” that tries to combine both!) 
All decent guidebooks define these in the opening pages or appendix, but those are the boring pages everyone skips over, right?  Here’s a review.  The definitions are from Freedom of the hills, 7th edition, Mountaineers Press.

(And, if this is all just a bit much for you, you can always use the old standby:  Jim Bridwell’s Casual Rating System.)

Class
A class rating describes the difficulty of an individual move on a route.  Note: A route can be almost all an easy 3rd class scramble, but if it has a single short bit of 5th class rock, that route is rated class 5.
Class 1:  Hiking on a trail
Class 2:  Simple scrambling, hands used occasionally
Class 3:  Scrambling, a rope might be carried
Class 4:  Simple climbing, often with exposure.  A fall could be fatal
Class 5:  Real rock climbing.  Protection, belays and rope are mandatory

Grade
A grade rating more describes time, and can be of any technical difficulty.  Grade ratings are properly given in Roman numerals.  Note: Experts can climb a grade VI route, like the Nose on El Capitan, in a single day, so ratings are somewhat subjective.
Grade I:  Route requires several hours
Grade II:  Requires half a day
Grace III:  Requires a full day
Grade IV:  Requires a full day, hardest rock pitch is usually over 5.6
Grade V:  Requires a day and a half, hardest pitch is usually over 5.7
Grade VI:  A multi-day adventure involving difficult free or aid climbing

Mazama grade
Mazamas climbs are graded to indicate approximate experience and/or ability levels required.  “A” level climbs are technically the easiest, and “E” level climbs are the hardest.
A - May require off-trail hiking, ice axe and crampon use on moderately steep slopes, and self-arrest.
B - May require off-trail hiking, ice axe and crampon use on moderately steep slopes, self arrest, glacier travel, and roped climbing.
C - May require off-trail hiking, ice axe and crampon use on moderately steep snow slopes, self arrest, glacier travel, and crevasse rescue skills, belaying, rappelling, and low 5th class rock climbing.
D - Ice ax and crampon use on steep snow slopes, glacier travel and crevasse rescue, self-arrest, belaying, rappelling and 5th class rock climbing.
E - Multi-pitch technical routes same as “D”, with high degree of self-sufficiency and proficiency using technical skills under high exposure, sharing high angle leads, setting protection and anchors.