A RAM file is a file associated with the RealPlayer software from RealNetworks. It serves as a playlist, and as a way to launch the RealPlayer application or plugin.
It is a plain text file, consisting of one or more URLs (usually just one), one per line. A URL may use HTTP, but for streaming services it may use Real-Time Streaming Protocol or the older Progressive Networks Media protocol. The referenced media files usually use RealMedia or RealAudio format.
RAM most likely stands for RealAudio Metadata.
Confusingly, the .ram file extension is also sometimes used for RealMedia format.