What is the difference between bystander behaviour and conformity?

Bystander behaviour is a broader term that describes the actions of a person observing a social event, e.g. a crime. Conformity is one of the factors that might influence bystander behaviour. For example, if you were walking down the street and you saw a thief steal an old lady's purse, your actions in response to this crime may be described as your bystander behaviour. One of the factors that influences your reaction is conformity. For example, if lots of people run to the old lady's aid, then you may feel the psychological pressure to conform and also help her, possibly due to a fear of how you might be judged if you do not help. Another example of a factor that might influence your bystander behaviour is 'the diffusion of responsibility'. For example, if there is a large group of people that observe the crime, it may be that nobody rushes to the old lady's aid because the sense of responsibility is psychologically shared amongst the group, and therefore each member of the crowd feels less pressure to help. Think about the remark 'nobody else is helping so why should I?' Overall, conformity and the diffusion of responsibility and many other factors work together to inform our bystander behaviour.