The U.S. government has ceded it's 19 year oversight of ICANN and therefore the namespace / numbering systems of the Internet.
Since it's creation in 1988, ICANN has been the corporation responsible for the management of the namespace of the Internet: IP and DNS. Resources on the Internet - such as websites - are accessed by an IP (Internet Protocol) address and the DNS (Domain Name System) converts easily remembered domain name addresses to IP addresses and vice versa: 190.00.00.10 to example.com etc.
Up until the 1st of October, 2016, oversight of ICANN and IANA - IANA assigns numbers on the Internet but is under the control of ICANN - was conducted by the (DOC) United States Department of Commerce and specifically the (NTIA) National Telecommunications and Information Administration of the DOC. This ultimately resulted in the U.S. having the final say on a critical aspect of the technical governance of the Internet.
The U.S. governments oversight of ICANN, and therefore oversight of the Internet's namespace, has long been a 'bone of contention' with other nation states who have demanded that oversight of the Internet's namespace should be ceded to the UN (United Nations) or an international organisation (discussed at NetMundial Initiative 2014). The U.S. government has never appeared willing to give in to such demands, but has acknowledged the criticism directed at it's ongoing oversight of the ICANN; releasing in 2009 the 'Affirmation of Commitments' to improve international oversight. ICANN has been criticised by commercial companies - Coca Cola etc - for it's continued TLD (top level domain) expansion program.
IANA predates ICANN and was created / controlled by Jon Postel; some likened Postel to an 'Internet God' due to his control of it's numbering system. It is one reason why ICANN was place in control of IANA; due to the unease some in the U.S. government had about Postel's power over the Internet. Likewise, nation states like Russia, China, France and Brazil are now expressing similar unease about the DOC's and ICANN's control of the Internet.
ICANN's contract with the United States Department of Commerce ("DOC") was outlined in documents such as: 'Memorandum of Understanding' (2006) and 'Affirmation of Commitments' (2009). The last of which outlined that the ICANN would have a multistakeholder governance model, but it still retained oversight by the DOC. On the 10th of March, 2016, the DOC signed an agreement to remove this oversight. Therefore, governance of the Internet's namespace moved to a purely multistakeholder governance model. This still has not satisfied some countries like Russia, but it is a significant step for the U.S. government to make, ceding control of the Internet's namespace.
Internet users are unlikely to notice any change whatsoever, as the ICANN largely operated with no interference from the DOC. The news of the removal of U.S. government oversight was met with dismay by political figures like Ted Cruz, who are concerned by the growing influence / power of foreign governments upon the Internet.