In everyday speech the word "law" is used in at least three senses:
1. Scientific law — a uniform statement about nature (e.g., the law of gravity). It describes what always happens; it cannot be broken.
2. Moral/natural law — principles of right and wrong (e.g., "killing innocents is wrong").
3. Positive law (municipal law) — the body of rules created and enforced by the State. This is the lawyer's law, and it is the subject of legal study.
The word itself reaches English through the Old Norse lag ("something laid down") and is closely related to "lay." A law, literally, is that which is laid down by a superior authority.