RA stands for RealAudio, which is a continuous and proprietary audio format developed by RealNetworks. It was designed to be a streaming audio format. It is a format to play audio clips within a web browser. RealAudio was first released in 1995, and the latest version is RealAudio 10, which was released in 2008.

RA is the audio codec, which can range form low bit rate to high bit rate formats for music. As a streaming audio format, it can be played and downloaded at the same time. In the past, it was used by many radio stations over the internet. However, it has become less popular and has given way to more other popular audio formats recently.

Files in RA format can be created by RealPlayer, containing audio data and reference online. The compression algorithm that RA files used is a proprietary Real compression algorithm.

The RA file comes with a file extension of .ra, .rm or .ram. A RealAudio player or other client programs usually include a web browser, or can be downloaded from the RealAudio or other web sites. If you want to deliver RA sound files on your own site, you will need a RealAudio server. The most common and famous RA player is RealPlayer. It is also known as RealOne Player, which is a proprietary cross-platform media player produced by RealNetworks. It supports a large number of multiple versions of proprietary RealAudio and RealVideo formats, and multimedia formats, such as MP3, QuickTime, MPEG-4, Windows Media and so on.

There are many programs that can be used to open RA files:
Windows operating system: RealNetworks RealPlayer, Web browser with the RealPlayer plugin
Linux operating system: Web browser with the RealPlayer plugin, RealNetworks RealPlayer
Mac operating system: RealNetworks RealPlayer, Web browser with the RealPlayer plugin