What is an advanced mission in Defense Grid?

There are a lot of achievements that require you to finish an advanced mission using only this or only that; but what exactly is an advanced mission?

I got some of these achievements by playing the "campaign" (first mode) of the C.H.A.S. maps for example, and I initially thought these were not advanced missions (and that instead the campaign challenge or impossible modes were)

Solution 1:

There is a post on Steam forums from a Defense Grid developer that said this:

The "advanced mission" phrasing is something we should have done better. Basically we didn't allow you to get certain achievements on the first four levels considering those levels to be "learning" missions. Out of Fuel and thereafter Every level is an "advanced mission." Sorry about the confusion.

(relevant bit in bold)

Hope that helps.

Solution 2:

An advanced mission is "Out of Fuel" or anything after it in the regular campaign, or anything in any of the other campaigns. Basically anything other than the first few missions where you have limited towers.

See the official response from here