No Audio Out Port?

[Daark]

Just put my imac together (had it a while but been so busy so now sorting it out) and i noticed 2 3.5mm jacks on the rear. One is headphones, is the other an Audio In and not out for speakers?
Find it weird there's only a headphone socket and not an audio out.

Confused.....

 

[aliensporebomb]

Sigh

The "headphones" jack is an audio out.

 

[Queso]

The headphones socket is also an optical audio out port.