Equity is the name given to the set of legal principles, in jurisdictions following the English common law tradition, which supplement strict rules of law where their application would operate harshly, so as to achieve what is sometimes referred to as "natural justice". It is often confusingly contrasted with "law", which in this context refers to "statutory law" (the laws enacted by a legislature, such as Parliament), and "common law" (the principles established by judges when they decide cases).
In modern practice, perhaps the most important distinction between law and equity is the set of remedies each offers. The most common civil remedy a court of law can award is monetary damages. Equity, however, enters injunctions or decrees directing someone either to act or to forbear from acting. Often this form of relief is in practical terms more valuable to a litigant; for example, a plaintiff whose neighbor will not return his only milk cow, which had wandered onto the neighbor's property, may want that particular cow back, and not just its monetary value. However, in general, a litigant cannot obtain equitable relief unless there is "no adequate remedy at law"; that is, a court will not grant an injunction unless monetary damages are an insufficient remedy for the injury in question. Law courts also enter orders, called "writs" (such as a writ of habeas corpus), but they are less flexible and less easily obtained than an injunction.