In Audio and Video compression, the term RGB means:

Compression is a technical process of reducing digital information to its essential components to reduce the amount of space it takes up. It is different from audio or video compression.

Audio or Video Compression:

• Video is a sequence of video frames involving huge amounts of data. With increasingly complex videos such as 3D movies and HD video quality, advanced image and video data compression becomes necessary.
• Audio and Video Compression techniques discard certain digital bits of information that are unnecessary or redundant or remove that digital information that might not be noticeable to human ears or eyes.
• The removed information is not completely discarded rather these data bits are restored at the receiving end. This technique is called lossy compression.
• Doing this helps in sending audio and video information without much loss in quality and with less channel bandwidth.
• Colour signals used in video production originated from three basic colour forms: Red, Green and Blue (referred to as RGB).

Hence, it can be concluded that the terms RGB means stands for Red, Green and Blue.