Intake and Exhaust??

I don't understand these terms in reference to growing. I mean if you have a fan blowing into your grow box, isn't that intake?? And a fan blowing out is exhaust?

In my case I have 4 computer fans in my box. On one side two are taking air from outside of the box and blowing it in. On the other side, two are taking air from in the box and blowing it out. Is that an intake/exhaust system? I always see people using tubing and I don't understand, my fans are just mounted directly onto circular drilled holes on my box. (same radius as fans)

That is intake and exhaust. The big silver tubes are ducting, and are normally only used if the fresh air source/the air dump are located slightly further away from the grow room than a regular fan can direct from/to.

lso, If using MH or HPS lamps, cooltubes help cool stuff down. These are hooked up to the tubes too, and will have a dedicated exhaust and intake too...

Ahh, gotcha. My intake is in my basement, and their is some dust/basement gunk kinda stuff on the ground. The intake fan is about 3' above the ground though, but should I still use some ducting to get cleaner air from upstairs? I don't know if small amounts of particulate matter could be harmful or not.

Maybe just throw a trap on it. An air filter of sorts.