What do you mean, " colleagues"?

Newcomer here, and a riveted one. I have been contacted by a neighbour wanting to be colleagues with me, and demanding some resources too, for good measure. But I cannot find anywhere, in-game or out in the web, about this kind of treaty. What does it involve? Which are the duties? And the benefits? I am very small compared to them, and we trade on regular basis, so they have a fairly good opinion about my little city-state of humans (they, on the other hand, are boar people or something, IIRC).