A bill is a proposed new law introduced within a legislature that has not been ratified, adopted, or received assent. Once a bill has become law, it is thereafter an act; but in popular usage (or even in moments of scholarly imprecision) the two terms are often treated interchangeably. Bills have a sponsor and sometimes cosponsors.
Bills can be divided into:
Sometimes other classifications of bills are used. For example, under many constitutions particular rules apply to appropriation bills. Commonly, in a bicameral system, the weaker chamber will have reduced powers with respect to appropriation bills than it has with other bills.
All bills originating in the U.S. House of Representatives begin with H.R. and all bills originating from the U.S. Senate begin with an S..
In the United States, bills can have the same number because every two years, at the start of odd-numbered years, the United States Congress recommences numbering from 1. Each two-year span is called a Congress, and each Congress is divided into two year-long periods called sessions.
In most constitutional systems, legislation once passed by the legislature requires the assent of the executive to become law (such as the Monarch, President or Governor).
In parliamentary systems this is normally a formality (since the executive is under the de facto control of the legislature), although in rare cases assent may be refused or reserved.
In presidential systems, the power of assent is used as a political tool by the executive; then it is known as a veto. In presidential systems, the legislature often has the power to override the veto of the executive by means of a supermajority.
In constitutional monarchies, certain matters may be covered by the royal prerogative (for instance in the United Kingdom these include as payments to the Royal Family, succession to the Throne, and the Monarch's exercise of their prerogative powers). The legislature may have significantly less power to introduce such bills, and may require the approval of the monarch or government of the day.