Yep, it’s what’s known as the “window decorations” - the title bar, icons for shrinking and closing the window, the window frames (so you can grab and resize them). The taskbar, though, doesn’t enter into it, since it’s not part of the window. You can either have it set to auto-hide, or just have the window overlap it.
Just take a screenshot of the full screen (and not just the current window) and it’s still at whatever resolution you have the screen set at.
You can also over-size the window: move it so part is off-screen, drag the opposite side over a bit more (up, down, left, right) then drag it so it’s almost all on-screen. If you accidentally resize it so big that the title bar no longer shows on-screen, just ALT+ENTER to go back to full-screen mode.