Realtime Transport Protocol is a data tranfer protocol defined to deliver live media to one or more clients at the same time. It requires an RTP server to capture, compress, packetize, and transmit the data over a network in real time. The transport protocol used by RTSP streaming.
Source: Sorenson User Guide
RealTime Streaming Protocol is the standard used to transmit stored media to one or more clients at the same time. Provides client controls for random access to the content stream. Requires an RTSP server. RTSP uses RTP as the transport protocol.
Source: Sorenson User Guide
These protocols are used when webcasting. They allow for a signal (such as a radio transmission) to be fed and distributed across a network as it is received.