container - a comfy place for audio and video

A container or wrapper format is a metafile format whose specification describes how different elements of data and metadata coexist in a computer file. https://en.wikipedia.org/wiki/Digital_container_format

A single file that contains all the streams (mostly the audio and video) and it also provides synchronization and general metadata, such as title, resolution and etc.

Usually we can infer the format of a file by looking at its extension: for instance a video.webm is probably a video using the container webm.