Net neutrality is the principle that individuals should be free to access all content and applications equally, without Internet service providers (ISPs) favoring specific websites.
Starting in the mid-2000's, the Federal Communications Commission (FCC) stepped in to resolve unfair situations. They went on to create the Open Internet Order in 2010, in order to “preserve the Internet as an open platform enabling consumer choice, freedom of expression, end-user control, competition, and the freedom to innovate without permission.”
Without the rules of net neutrality, a plethora of issues arise. Services that an ISP controls can be given priority, making the other product seem worse to an unsuspecting consumer. Third-party companies that run these services would be able to bribe the ISPs to boost the availability or speed of their product. But not only services would benefit, the ISPs could charge additional fees for users to access certain websites. The video below is a general explanation of net neutrality in it's entirety, but contains additional issues and metaphors.
2014 was a big year for Net Neutrality. Verizon had a lawsuit with the FCC, and the court ruled that the FCC had to reestablish the rules for ISPs. In April, the FCC's ideas were leaked, and the plan was to ban discrimination against websites but allow a company to bribe ISPs. After a period of public backlash against business paying to be promoted, the FCC voted to put strong net neutrality rules into place in February 2015.
The FCC had some legal challenges since then, but the appeals court have upheld the FCC's new set of laws.