What are the differences between informal and formal organization?

Question

What practices are considered informal?

Which are considered formal?

Perhaps informal and formal practices are really just the ying and yang of organization?

Answer 1

An organization is a group based on membership with common goals, beliefs or practices.

Formal and Informal deal with the degree binding of membership, of commitment, oaths, control of authority or leadership, structure, facilities, fees, duties, and activities.

A third category would be on a more organic nature, or more as an organization based on interaction where each member is responsible for their own participation and actions.  Operations and coordination are through lateral communication and mutual input and planning.  Giving room for independent response or action to carry out main objectives or to maintain a current desire condition.   

The latter is more of an organism  than an organization.  Organization function more on the control, leadership, and effort of the normal 20% (80%) ratio.  The other functions on local pockets of members working together with no specified leader because it is driven by goals rather than orders.

Answer 2

Lets start with an organization. It is a group of individuals striving to accomplish a common goal, and does so by distributing tasks.

A formal organization is a group that has a set of rules, code of conduct, where the workings of the group is formalized.
Let's try a few examples:
At work there are rules to how you behave, at work. Work is a formal organization.
When attending a wedding there are rules governing the conduct of the participants. A wedding is formal.
A demonstration. Could be argued to be formal.

An informal organization is when said group does not have outspoken rules/codes of conduct in order to accomplish it's common goal.
A group of friend gather at a bar, casually, and they are just hanging out. Informal group.
A riot. Informal.

A few last words on this: the line between informal and formal organizations is a bit blurry. In many ways it also connects to the feeling of the organization. An informal organization can be just as effective or innefective as a formal one. A formal organization can be just a successful/unsuccessful as an informal.