5DIII..AF Assist beam..AF Illuminator

[maass]

Hi,

I am new to Camera world.
Can anyone make me understand What is AF Assist beam ?
Is it the same people are complaining about a AF Illuminator.
Below is from 5DIII specifications page.

AF Assist Beam
(1)   Enable

With an EOS-dedicated Speedlite, AF-assist beam is emitted automatically when necessary.

(2)   Disable

(3)   IR AF assist beam only

* No AF-assist beam with flash bursts.

[Grum]

Some cameras have home built in, with the 5D mk III you need to have a flash gun in the hotshoe. I don't know why Canon don't include them tbh.