What is a omission in the criminal law?
In general in law, an omission is a failure to do something you should have done. It might have been something you had to do to comply with a contract (I am not talking about a fundamental breach) or something that you should have done to comply with the law or something you should have done for reasons of health and safety or the reasonable management of risk or it could just be something that is normally done as part of the custom and practice in a given industry/sector and that was not done on this occasion.