Just as the Masthead is a fixture of mobile applications, the Chyron is a bar docked to the bottom edge of the viewport which provides another always-present container in which to place items, from navigation to advertising.
The name comes from the overlays for labeling who is talking on interviews, what channel is being shown, and so forth in TV production (and other motion video). This is called a "lower third" generically, and is referred to as a chyron (sounds like kai-ron) in much of the world including the US, due to an early and popular machine to create them.
The chyron is a bar as wide as the viewport, and generally about as tall as the Masthead.
This container can be used for key functions on the page, such as submit buttons, or for app-wide functions that need to remain visible at all times.
In iOS, the Fixed Menu occupies the Chyron space.
When more than one function occupies the Chyron, it is usually best to separate them with thin vertical rules
Labels must follow the guidelines outlined under ??? to assure they are actionable, direct, and clear.
When the function in the Chyron takes place within the page, such as re-synching data, there may be a delay. The Chyron will gray out, cannot be selected, and should change wording to indicate it is working. The icon should also animate, or be replaced with a delay indicator to show that it is functioning, and the grayed out state is temporary.