What do we mean when we speak of common law?

Two technical terms of great importance that are likely to puzzle the novice are common law and equity. The law of England may be said to be composed of three great elements. They are legislation, common law and equity. Before the Norman conquest in 1066, the English Legal System involves in a mass of oral customary rules which verified according to region. But Wales and England could not rely on customs. So, a more organised system of court appeared after the Norman conquest in 1066. This is because, when the English throne was gained by William the Conqueror, he began standardizing  the law as he established a strong central government. William set up the Curia Regis and appointed his own judges. Common law was developed by Henry II when he divided the country up into circuits or areas for the judges to visit. Later, the judges chose the best customs which were to be …(short extract)