df -h command

I wanted to see all the comumed of volumes in an aggregate

i ran df -h and saw the following 

Filesystem                                            total             used                   availcapacity                               Mounted on
/vol/ExchMngrsDb7/                            1295GB      1252GB              43GB       97%                             /vol/ExchMngrsDb7/
/vol/ExchMngrsDb7/.snapshot        68GB        485GB            0GB       713%                       /vol/ExchMngrsDb7/.snapshot

What I dont Understand is the .snapshot

Total is 68GB 

Used is 485 How ?

Availablecap is 0GB 713 % ??

can any one explain me this ?