[pocketjacks]

I am getting back into limit after some time off, and have been reading a lot of the posts here and keep seeing facts such as
"villain is 33/4/0 after only 16 hands"

Stuff like this.
Can someone please explain what the 3 numbers represent.
What they mean?
Finally how do I find them for my opponents? Do I need to buy Poker Tracker?

Thanks in Advance.