The WebM video format is an open and royalty-free multimedia container format developed for web usage. It is designed to efficiently store video and audio streams, using the VP9 video codec and Opus audio codec for compression. WebM files are widely used for web-based applications and online streaming due to their high-quality compression and open standards, making them compatible with various browsers and platforms. The format is supported by major web browsers, making it a popular choice for delivering high-quality, efficient video content over the internet.