In the United States, the Bill of Rights is the first ten amendments to the Constitution. The purpose of the Bill of Rights is to provide specific freedoms to citizens and limit the power of the government.
When it's capitalized, the Bill of Rights refers to a specific statement of rights, like the one that precedes the US Constitution. With lower-case letters, a bill of rights is a more general formal statement of rights and freedoms for a group of people. The US Bill of Rights was ratified in 1791, and it guarantees — among many other things — the rights of free speech, freedom of religion, and trial by jury.