Server ticks?

So, I've been working with a save-cycle system to handle async saving to a database and I'm kind of confused as to how long a server tick is?
Since the BukkitScheduler takes it's periods in ticks.
I'd appreciate it if someone could give me an approx in milliseconds or seconds.
Thank you.

EDIT: Nevermind, found it. 20 ticks = 1 second.