Net neutrality is the concept that the internet should be free and accessible for all. What is defines is that ISPs have a moral duty to uphold the freedom of information on the internet. Big companies like Verizon or Time Warner Cable must have a hands off approach when it comes to what websites or service that users can access. This forms the core of the debate around this topic but there are other issues like net privacy and freedom of speech etc.
Large media companies are diabolical in the way they would want to regulate internet traffic. For example they would love to charge a user extra money in order to use Google or Facebook or Amazon. In several cases such as Comcast they have products that compete directly with numerous websites which also offer the same service. Comcast competes with Netflix as well as Hulu and other video streaming websites for customers and can abuse their power to either block these websites all together or slow bandwidth connection to them or even charge people more money to access them.