流媒体（Streaming media）是指将一连串的媒体数据压缩后，经过网络分段发送数据，在网络上即时传输影音以供观赏的一种技术与过程，此技术使得数据封包得以像流水一样发送；如果不使用此技术，就必须在使用前下载整个媒体文档。串流传输可发送现场影音或预存于服务器上的影片，当观看者在收看这些影音档时，影音数据在送达观赏者的电脑后立即由特定播放软件播放（如Windows Media Player，Real Player，或QuickTime Player）。

流媒体文档一般定义在bit阶层，因此串流封包并不一定必须按照字节对齐，虽然通常的媒体文档都是按照这种字节对齐的方式打包的。

Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a provider. The verb "to stream" refers to the process of delivering media in this manner; the term refers to the delivery method of the medium, rather than the medium itself, and is an alternative to file downloading.