"Chrome" is the term for the OS provided border around the window. It offers anchoring points to resize the window; a place to click for dragging; as well as the buttons for closing, maximizing, minimizing. Without chrome, you can't do any of those things, so the window would be fixed in size and place. To get that functionality back, you have to manually code it into the app.
Fun fact: Chrome, the browser, is named ironically. Compared to other browsers at the time, Chrome had almost no chrome around the window content. That was one of the product's signature differences: its UI was so simple that there almost wasn't any UI, allowing users to focus entirely on the content. Thus, calling it Chrome was very funny.
The 2013 Chromebook Pixel followed this naming theme. The screen was so dense that you couldn't see the pixels.
