I've been googleing icons for a new forum of mine, my plans are to make money from the forum via adsense. With the following agreement, am I allowed to use them on my forum without linking back? License:
You need to get permission. If your site takes in any type of income (or attempts to via adsense), it is considered commercial.
My take on this is that "commercial" is defined by attempting to sell the icons bundled with software, websites, scripts, etc. I may be wrong though.
It is certainly a commercial use you are planning. The term "commercial" is not subject to one's personal interpretation. It has a very clear meaning in the law and mjewel has explained it pretty plainly.