In parliamentary systems, of three branches of government—executive, legislative and judicial—the legislative branch is the most powerful. In other forms of government, such as democracy for example, the three branches of government are equal in power. When a parliament makes a law, called an , it is ing on the other two branches of government. Acts are made by a majority vote of the legislature. The exact process differs in different parliamentary systems. In a bicameral (two-chamber) system there is usually a lower house (such as the House of Commons in the UK) and an upper house (such as the House of Lords). A new law starts out as a bill, usually in the lower house. It must pass both houses before it can become an act. Other systems use a unicameral or one-chamber legislation. In either system, an act becomes the law. Judges and the courts have almost no authority to challenge the validity of a law.