A symbolic link (symlink) is a file that’s a pointer to another file (or a directory). One use for symlinks is to have a big file be in two places without using up twice as much space. ln -s /gpfs/home/abc123/scratch/big_file /gpfs/home/abc123/work/big_file
You can see another use in your home directory on the cluster: ls -l scratch gives us this directory listing:
lrwxrwxrwx 1 mjw5407 mjw5407 21 Jun 22 2011 scratch -> /gpfs/scratch/mjw5407.
The l right at the beginning of the line tells us that scratch is a symlink to /gpfs/scratch/mjw5407.
And if for some reason you see that scratch is not a symlink but a regular directory, something has gone wrong. (This happened recently to a cluster user. Check your directory listings!)