In reply to leeoftroy: The adjectival grade reflects the fact that the seriousness, or severity, of a route is brought about by a combination of the difficulty of the climbing, how sustained it is, and how well protected.
So, a route where the hardest climbing is 4a would normally merit Severe, cos climbing rock that hard is pretty Severe, innit?
But if that 4a climbing suddenly has no gear then it's a much more severe prospect. In fact it's Very Severe. Make sense?
Doing 4c moves is a Very Severe undertaking in itself, even if the gear is fine, so those routes get VS just for that.
In general, the 'standards' are:
Severe 4a
HS 4b
VS 4c
HVS 5a
E1 5b
etc etc
With experience, you'll find that you get quite a lot of information out of the grade. For the grade list given above, any deviation by 2 grades or more are unusual routes -- if the technical grade is low (VS 4a or E1 4c for example) then it's usually very poorly protected. If the technical grade is very high (e.g. Severe 4c) the the hard move is probably getting off the ground i.e. it's relatively hard to hurt yourself.
Common grades that deviate from the above are:
S 4b -- one move wonder, usually well protected.
VS 4b -- sustained and well protected I often find
VS 5a -- only one 5a move and the gear is right next to you. Usually.
HVS 4c -- A funny one. Badly protected in the Peak. Steep, sustained and well protected at Swanage.
HVS 5b -- not climbed enough of these to comment.