the practice or principle of giving the group priority over each individual in it.

Cooperative work done by a team. Teamwork is the concept of people working together as a team.

I think this expression translates best what is meant here. The word "collectivism" has another meaning (political theory of collective control over production and distribution), that should be avoided. Some examples, in similar contexts:

IRRODL: Blended Learning and Sense of Community: A Comparative ...
Research evidence suggests that low sense of community is related to two ... The research hypothesis was that sense of community would be strongest in the ...
www.irrodl.org/content/v5.2/rovai-jordan.html


Into the Blogosphere: Rhetoric, Community, and Culture of Weblogs
...Blogs as Virtual Communities: Identifying a Sense of Community in the ... It is the sense of community that distinguishes virtual communities from mere ...
http://blog.lib.umn.edu/blogosphere/blogs_as_virtual.html



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Note added at 21 mins (2006-02-25 13:37:12 GMT)
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Another good reference:

Sense of community - Wikipedia, the free encyclopedia
Sense of community (or psychological sense of community) is a concept in social ... Among theories of Sense of Community proposed by psychologists, ...
http://en.wikipedia.org/wiki/Sense_of_community