To collaborate is to work on a mutually shared goal with the intention of creating one or more specific products together.
Collaboration can be described by identifying shared goals or shared plans.
The intended goals of collaboration may complexly contain separately useful goals or products. However, collaborators perceive value in a unified pursuit of developing those goals or products(s). Their unified pursuit creates some (lesser or greater) degree of shared investment; this often requires significant trust and/or accountability.
Collaboration often occurs informally and unofficially. However, a collective may officially (and complexly) assign subordinate work to subgroups.