Do it have any name to call this little thing?
it's a status bar. it's not specific to osx, all browsers have one.
it used to show the url of hovered links, status of requests, etc and then some add-ons/plugins started using it to show information.
Recently it's been reduced to a something like a tooltip in most browsers (it only appears on mouse over links or when something is loading, etc).
This is a status bar.
In Cocoa programming you can create this by adding a custom view on the bottom of a window and using a text field to show information as required.
Note that in OS X programming, the "Status Bar" (class NSStatusBar
) refers to the the rightmost portion of the system-wide menu bar, with all the little icons, the clock, spotlight and so on. User-facing copy however uses "Status Bar" as a term for a horizontal area on the bottom of windows that contains auxiliary information (e.g. link URLs in Safari, or item counts and sizes in the Finder).