(1) In HTML, the container is the area enclosed by the beginning and ending tags. For example encloses an entire document while other tags may enclose a single word, paragraph, or other elements. In HTML code, all container must have a start and stop tag to close the container. Without a stop tag the start tag will apply to the entire document.
(2) In software development terminology, the word container is used to describe any component that can contain other components inside itself. Examples of containers include Java applets, frames and windows.
(3) In video terminology, container is often used to specifically describe a container format.