A webcast is a media presentation distributed over the Internet using streaming media technology to distribute a single content source to many simultaneous listeners/viewers. A webcast may either be distributed live or on demand. Essentially, webcasting is “broadcasting” over the Internet.

The largest "webcasters" include existing radio and TV stations, who "simulcast" their output through online TV or online radio streaming, as well as a multitude of Internet only "stations". The term webcasting usually refers to non-interactive linear streams or events. Rights and licensing bodies offer specific "webcasting licenses" to those wishing to carry out Internet broadcasting using copyrighted material.

Webcasting is also used extensively in the commercial sector for investor relations presentations (such as Annual General Meetings), in E-learning (to transmit seminars), and for related communications activities. However, webcasting does not bear much, if any, relationship to web conferencing, which is designed for many-to-many interaction.