Every role we play and every value we hold has a number of associated ideas called norms (short for "normative " or "normal").   A simple definition of a norm is that it is an expected, socially-acceptable, way of behaving in any given social situation. Like the associated concept of values. norms differ from individual to individual and society to society. 

However, whereas values are very general guidelines for behaviour, norms compliment values because they represent very specific rules that govern our behaviour in particular situations. As Thio ("Sociology") puts it:

"While norms are specific rules dictating how people should act in a particular situation, values are general ideas that support the norm".

In basic terms, there are three types of norm we can distinguish:Giving flowers on a birthday - an example of a folkway

a. Folkways: These are fairly weak kinds of norm.

b. Mores (pronounced "more-rays"): These are much stronger norms and a failure to conform to them will result in a much stronger social response from the person or people who resent your failure to behave appropriately.

c. Laws (legal norms): A law is an expression of a very strong moral norm that exists to explicitly control people's behaviour.

From the above, we can see that norms can be both "written" (or codified) as formal, official and legal norms and unwritten (in which case they are informal or unofficial norms).

The concept of norms is not only useful as a means of showing the various ways that human behaviour is structured. It also helps to illustrate one of the ideas noted earlier concerning the subject matter of Sociology.

You will recall that one of the problems we identified was that society does not have a physical existence (we cannot see it, for example), yet sociologists argue that it affects our behaviour because it is a force. We can demonstrate the existence of this force using the concept of norms.This man used an  illegal drug.
But he didn't inhale which, apparently,
makes all the difference...

Although we cannot see norms, sociologists argue that they act on us in various ways because they represent expected and acceptable ways of behaving in society. If this is the case, we should be able to experiment with norms of behaviour to see the possible effect of disrupting normative expectations (the behaviour people see as normal) on people's behaviour. In basic terms, if norms exist as a "force", when we break or disrupt them we should see a clear response from the people around us...