I am confuse or mis-understood. Can someone explain how to read "c0t1d0s3" under filesystem?

Have you tried mounting the file system? ie,
mount /dev/dsk/c0t1d0s3 /path/to/mount/point

Yes it is mounted onto /oraclesw but do those letter c d t s words have meaning. Is d is for disk and s is the slice(partition)?

controller
target
logical device (lun)
slice

in addition to stickman.
it means that depending on what your disk is (internal/external) it'll be hanging off a certain controller, say X. A controller will have a specified number of targets on it e.g. Y. On this you'll have a disk hanging off it again, say Z and on the disk you'll have slices (8 i think it is.. it's been a while since i've had to format) say slice N.

so put that all together and you'll have cXtYdZsN..

werd? Yes. But damn.. when you've got 80 disks hanging off 7 different arrays on a highend server... it becomes neccesary.

hth.