Yeah, the definition we are talking about is "Carbon Offset", and this pretty much sums it up we think:
"A financial donation or other act that aims to remove a certain amount of carbon dioxide from the atmosphere, to compensate for another carbon dioxide emitting activity, e.g. a flight."
(taken from http://www.carbondescent.org.uk)
We plant a tree for every hosting account we sell and for every year you stay with us thereafter. You get to Carbon offset your Website and we all have loads more lovely trees on the planet. Hurrah!