What is an edge server / router / device?

Solution 1:

An edge server, in a system administration context, is any server that resides on the "edge" between two networks, typically a private network and the Internet. Edge servers can serve different purposes depending on the context of the functionality in question.

Some examples:

• Security Context: usually a firewall, router or similar device
• Application Context: a web load balancing server
• Mail Context: some kind of hub server that forwards mail on to internal servers

Usually an edge server has some kind of gateway responsibility for the internal/private network.

Solution 2:

It's usually a caching proxy server, located near the user accessing the data, used to improve bandwidth and latency to far away users while lessening the load on central servers.

http://en.wikipedia.org/wiki/Content_delivery_network

Solution 3:

By EDGE do you mean Enhanced Data GSM Environment? It pretty much stores data files on remote servers with the specific purpose of streaming them over the internet.

Edge Server – (Enhanced Data GSM Environment) Storage of data files on remote servers specifically designed for streaming over the Internet. EDGE is a faster version of GSM wireless service. EDGE enables data to be delivered at rates up to 384 Kbps on a broadband. The standard is based on the GSM standard and uses TDMA multiplexing technology. Source

Solution 4:

A Edge server can also be a element in live streaming topology. It's a server that has the role of a relay, it get the stream from the "core" server, and transmit it to the clients, this allow to bypass de bandwidth limit of the core, the clients won't use directly the core server :

[CORE] ----------> [EDGE] ----------> [Clients]
        |                  '--------> [Clients]
        |
        '--------> [EDGE] ----------> [Clients]
                           '--------> [Clients]