What is the /data/db folder in OS X?

Question

I'm using OS X 10.6.8 and cleaning up my almost full hard-drive using the free tool Disk Inventory X. I stumbled upon the /data/db folder which weighs more than 600Mb. Before deleting some of its content I'd like to understand: what is it? Is it system critical? Note that I'm a web developer and I often create databases on my computer. It seems that the name of the files matches some of the databases I previously created, but not sure it's a 100% match.

Answer 1

On my snow leopard system there is no such directory. I guess custom installed.

do a

> sudo -s 
> ls -alR /data/db
ls: /data/db: No such file or directory

Answer 2

It was custom installed by MongoDB, this the default folder for writing database. So it has nothing to do with OSX.