Newton's First Law of Motion, also known as the Law of Inertia, states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This fundamental principle introduces three key concepts: inertia, which is an object's resistance to changes in its motion state; force, which is any push or pull acting on an object; and motion state, which refers to whether an object is at rest or moving with uniform velocity.