what's /dev/shm

[Suhas Kamble]

Hi,

Any ideas how the size of /dev/shm is decided? Can we increase it by any 
way?
We're testing it to mount as a filesystem and see if we can use it for 
temp area for one of our application. We're running RHEL ES3.0

mount -t tmpfs /dev/shm /mnt/shm

the output is

/dev/shm              3.0G  8.0K  3.0G   1% /mnt/shm

has anyone used it? Are there any security hazards?
Any inputs towards this will be greatly appreciated. 
regards,

~Suhas