Off Canvas items live outside of your viewpoint and only appear when you call them in with an action.

There is a cute little Off Canvas Sidebar in Montana that will slide open when you click a small icon on the left of your Header Menu. This Sidebar is also a Sticky one that follow you when scrolling down on your page and since the button to call it is also placed on a sticky header, it will come out anytime you call. This is a perfect nest to places convenient boxes like User Menus or even Shopping Carts.

It is very useful and it is a way to add animation effect to your site too, without taking an inch of your precious screen display.