An ancient time people were free. They ruled by themselves. When people lived with group then they made rule to manage their behavior and conduct. Then after gradually they became ruler and ruled. Senior person of the group might be setup the rule and regulation at earlier time. The society gradually developed and changed. In the changing context rule and regulation also be changed. In course of time various laws were enacted and amended. All activities of natural persons as well as artificial persons are regulated and guided by laws. Law is a formal mechanism of social control. By changing nature of law there is not universal definition of law. It depends on the contexts and perceptions.
In general, the term 'law' means a set of rules. Those rules are made by the authorities. Public laws are made and implemented by state authority. But private laws are imposed by the party in according to existing laws.
Law is an English word derived from the Stoic term 'Lag'. It means Stable and universal. In general sense, law means the command of the sovereign power to manage and regulate the external human activities. Law is a general term and has contextual meaning. It is used in different places within different senses and names. Still, it is impossible to define it in a single term. Many literatures have been created, many books have been written by many writers on this topic. However, it has not unanimous definition.
Here is better to cite an expression made by Lord Lloyd, who says "Since much juristic ink has flowed in an endeavor to provide a universally acceptable definition of law, but with little sign of attaining the objective".