There are many pieces to a streaming media system. Encoding tools are used for compressing the media into a format suitable for delivery over the Internet. Servers make the compressed files and live streams available to many people. Players connect to the servers and get the media.
Additionally, there's a lot of technology under the hood. Codecs are the compression/decompression routines used by encoding tools and players. File formats are shared by encoding tools and servers to generically store encoded streams. Players and servers need shared protocols for streaming the data.