Actus reus means action or conduct which is a constituent element of a crime, as opposed to the mental state of the accused.
Actus reus is the Latin term for the "guilty act," which refers to the physical element of a crime, which includes either a voluntary physical act or a failure to act when there is a legal duty to do so.
It's also one of the two essential components of most crimes, with the other being mens re, which is the guilty mind or criminal intent.
For a crime to be committed, a person has to perform a voluntary action or an omission, and the act must also be unlawful and connected to the resulting harm.
The key aspects of actus reus is the physical act or omission as it refers to the physical deed or the failure to act when legally required to do so.
For example, in a theft, the physical act is the act of taking someone's property; in a case of negligence, the actus reus may be the failure to act to prevent harm when a legal duty exists.
And the act has to be voluntary.
As it does not include actions that are the result of reflexes, sleepwalking, seizures, or any other state in which the person is not in control.
And in many cases, the act has to be directly connected to the criminal result.
For example, the physical act of using a weapon is the actus reus in an assault case.
And criminal law also punishes actions and not thoughts alone, which is also why actus reus is a crucial element.
A person can't be convicted of a crime that is based soley on their intentions; they have to also have performed a prohibited act or an omission.