What is a fan header?

[brianmanahan]

Is it a power/sensor for controlling fans? I was thinking about getting a case w/ front and back fans, and wondered if only 1 fan header on the DS3 1.3 would be a problem.

 

[Heidfirst]

a fan header is the 3 or 4-pin socket on the mobo that supplies power to a fan.
Some additionally can read the fan rpm (if signalled) & also have the voltage on them varied hence control fan speed.
When I had a DS4 it was 1 of the things that I would have preferred more of plus the Gigabyte fan control is pretty primitive (currently using an abit QuadGT with 5 headers & better fan control).
It is possible to power fans directly from the PSU or via a fan controller though so it isn't necessarily a drawback.