Equity is a distinct branch of judge-made law. It is on one view a rival to the other branch - the common law. On another view, it is just a strand in judge-made law along with the common law, operating alongside and interacting with the common law according to well-settled rules governing this process of interaction.  It was developed due to the injustice cause by the rigidity of the writ system at common law. The aggrieved party would apply to the King, later to the Chancellor, for a more flexible remedy. Equity later developed its own rather rigid rules.  Equity also means "fairness", "justice" and "impartiality".
Before 1066 there was no centralised system of law in England. Each area observed its own customary law which was administered by local courts. After the Norman conquest, the administrative and judicial functions were taken over by the king's council. One of the most important members of this council was the Chancellor who had the responsibility of sealing each writ before an action could be commenced in the king's courts. The Chancery was then established and assisted with the judicial business of the council.
Over the next three hundred years the courts of common law developed and consolidated their respective jurisdictions. Important matters were dealt with by the court of King's Bench. Less important matters were initially dealt with by the Court of Common Pleas. A third court, the Exchequer, handled revenue matters. These courts administered the common law.  One of the case such as Walsh v. Lonsdale (1882) can likely explain the meaning of common law, Lonsdale agreed, in writing, to grant a seven years lease of a mill to Walsh at a rent payable a year in advance. Walsh entered into possession without any lease having been granted, and he paid his rent quarterly, and not in advance. Subsequently, Lonsdale demanded a year's rent in advance, and as Walsh refused to pay, he distained.