I live with three very different people; that's three, including 
myself. We are all different, and we decided to try living together as 
a social experiment. Personally, I am interested in decentralized 
social and governmental systems: distributed power, distributed 
decision making, etc. I am an optimist in that I believe that a 
"sufficiently large" collection of people "educated" on a particular 
topic will collectively make statistically wise decisions on that 
topic, no matter the variations in individual decisions. To me, this 
seems one (of possibly uncountably many) functional definitions of 
democracy. It may come off as elitist (and to some, that's okay) due to 
the use of the term "educated" but this in no way refers to social, 
economic, or any other form of privilege. I use the term very generally 
to connote experience, knowledge, and understanding of a certain topic. 
Of course, there is that ambiguity "sufficiently large"...
Anyway, I digress. Social experiment. Understanding of social systems 
via practical experience, with willing participants that are aware of 
the process, the goals, etc. We have hit the "growth" stage now, i.e., 
problems. And in a discussion with one of the members today, I was 
asked how I define "community." This was an interesting question... I'm 
always talking about this concept, this abstraction; I'm always 
listening to others talk about it. We all seem to agree that we're 
talking about the same thing, but here was my chance to see, in fact, 
if that's the case. I paced around the room for a while, like an 
autistic child about to make a break through. Here's how I defined it:
A community is a group of entities that interact for the common benefit 
of all entities in the group through exchange of information between 
entities and the compensation for deficiencies and/or efficiencies of 
individual entities.
I'd never thought of it like this before, and it really took me by 
surprise: community dynamics is an engineering problem! Of course, I 
say this with all the humor it deserves ;-) And this revealed the 
nature of the problem between two of the individuals in our social 
experiment: two of us are unwilling to compensate for each other's lack 
for the common benefit of the group. We are therefore failing as a 
community, in that we cannot satisfy the definition. This awareness was 
a painful moment for me, as I have been greatly looking forward to this 
adventure. It's early still, so there is hope. The biggest difficulty 
we may encounter is motivation: if we don't feel in our bones that we 
have to work with these differences in order to survive, we may 
not put in the required effort.
Community interaction is not an endeavor of self. In the "West", we've 
got plenty of that! We are all about the individual. I find this 
particularly true of Americans, and have been guilty of such for much 
of my life. We feel that many (all!) sacrifices somehow lessen "the 
self" and are therefore tantamount to the complete violation of our 
most precious principles. Practical experience in communities that meet 
the requirements of the functional definition above show us something 
quite the reverse: personal sacrifice for the benefit of all improves 
the quality of life for all members of the group, and sometimes 
especially for the one who sacrificed. 
In these "modern", post-tribal times and for the most part, we are no
longer bound to each other by the glue of survival needs, forced to
live in communities and tribes, getting along out of necessity. As
such, it may be that Quality of Life has become the new definition of
Survival. And in fact, our survival as a sane and happy society may
require that quality of life be perceived as such.
Curious now, I have looked up the definitions of community on WordNet:
* community -- (a group of people living in a particular local 
area; "the team is drawn from all parts of the community")
* community -- (a group of people having ethnic or cultural or 
religious characteristics in common; "the Christian community of the 
apostolic age"; "he was well known throughout the Catholic community")
* community -- (common ownership; "they shared a community of 
possessions")
* community -- (a group of nations having common interests; "they 
hoped to join the NATO community")
* profession, community -- (the body of people in a learned 
occupation; "the news spread rapidly through the medical community")
* community, community of interests -- (agreement as to goals; 
"the preachers and the bootleggers found they had a community of 
interests")
* residential district, residential area, community -- (a district 
where people live; occupied primarily by private residences)
* community, biotic community -- ((ecology) a group of 
interdependent organisms inhabiting the same region and interacting 
with each other)
I particularly like the last one, from the ecological point of view. 
Being an adherent to a Tibetan Buddhist school of philosophy, I enjoy 
the point of interdependence.