Current shares- valid hashes for a lower difficulty of the block(iffy on why)
Score- Not a clue!
Every hash you do for a pool has one of the three following outcomes. The hashed result is...
1) Smaller than the current difficulty's target == you found a block.
2) Smaller than the lowest possible difficulty's target == you found a share.
3) Larger than the lowest possible difficulty's target == try again.
Holy-Fire explains above what Score means.