Diminished responsibility is a legal defence used by people on trial for murder. It means that the person being tried did not have the same level of responsibility for the crime that a normal person would have. For example, if a person has been very unwell and was in a confused state when they committed the crime, they might be able to use diminished responsibility to show they weren't in full control of their actions. This means they could get a reduced sentence, or even be found not guilty of the crime.