The European Internet Exchange Association (Euro-IX) defines an Internet Exchange (IX) or Internet Exchange Point (IXP) as a technical facility that enables the interconnection and exchange of Internet traffic between more than two independent Autonomous Systems.
An Internet Exchange lets Internet service providers (ISPs), content delivery networks (CDNs), and other network providers exchange Internet traffic with one another, typically on a cost-neutral basis. Connecting into the infrastructure with a port allows each network to connect to other networks and share traffic, also known as peering.
Watch Euro-IX's video that explains what an Internet Exchange Point is and how it works.
The video is available in several other languages at the Euro-IX Youtube channel.