Some guesses, some based on what Ian and Co. has said.
Run Block- Nothing, as far as I know
Pass Block- Nothing, as far as I know
Jumping- Vertical leap, most apparent with receivers and DBs
Kick Return- Ability to catch a kick, pretty much. Avoid muffing punt returns
BC Vision- Ball carrier vision- CPU only, you take over for this attribute
Run Block Str- Power... ability to move a defender once engaged
Run Block FW- Ability to make contact, not get knocked over
Pass BLock Str- Ability to hold up to a bull rush
Pass Block FW- Ability to fend off a finesse move
Awareness- Catch-all for mental aspects of the game.
Man Coverage- Awareness when in man coverage
Zone Coverage- Awareness when in zone coverage
Awareness's effect on defense has been mostly mitigated by Zone Cover, Man Cover, and Play Recognition, but I think it's still there for some other minor checks.
Don't think so, I think it has to be natural.
Margin of error on the kick meter I believe, but don't quote me... considering there doesn't seem to be a potential for "error" on the kick meter at all:P