What is Marketplace Fairness Act?

Legal Definition
The Marketplace Fairness Act is proposed legislation pending in the United States Congress that would enable state governments to collect sales taxes and use taxes from remote retailers with no physical presence in their state. Identical versions were introduced into both the United States House of Representatives and the United States Senate during the 113th United States Congress. During the previous, 112th Congress, a bill (S. 1832) was considered but expired without enactment.

The current bill (the Marketplace Fairness Act of 2013) was introduced on February 14, 2013, in the House as H.R. 684 and in the Senate as S. 336. It was introduced a second time in the Senate as S. 743 on April 16, 2013 and was passed there on May 6, 2013. All three bills are virtually identical and would allow states to require online and other out-of-state retailers to collect sales and use tax.
-- Wikipedia