In legislative terms, a bill is a proposal
a. that has reached committee for debate.
b. made in the senate.
c. made in the house of representatives.
d. for any law.

Before a bill is a bill, it is an idea, then a bill, and from there it needs a sponsor, or a few, from the House of Representatives, and from there it is then introduced into the House of Representatives, then it goes to the Committee who revise, review, and research the bill. It's then sent back to the House, debated/voted upon, where it goes to the Senate, from the Senate to the President, he signs it, and thus the bill becomes a law.