Containers are at the core of Bootstrap's grid system, and they typically form the root of all Bootstrap pages. A container is exactly what it sounds like—an element for holding all other content within a section of a page. By remaining toward the top of the element hierarchy, a container provides the base for how the section contained within it is rendered. You can think of a container as representing a canvas in a browser window for your content. All this content will be displayed on this canvas, which in turn can transform based on its environment. Unless explicitly specified, your content will never creep outside of this canvas, regardless of the viewport. A container can apply to the entire contents of a page, where you would have one root container element, or to different sections of a page, where you would have numerous container elements on the page.

There are two types of container classes provided by Bootstrap: container and container-fluid.