Wrappers are used to enclose large areas of content. There are a couple of versions,
o-wrapper--main for the main content on the page, and
o-wrapper--wide for a wrapper that stretches the full width of the page instead of being constrained to 1200px as the normal wrapper is.
Wrappers are often given the class
.o-grid in order to be the container for
div with the class
.o-wrapper--main should also have the class
.js-wrapper--main in order for it to pick up on the page height fix.
<div class="o-wrapper o-wrapper--wide">...</div>
<div class="o-wrapper o-wrapper--main js-wrapper--main">...</div>