The menu button with three horizontal lines: ≡
When pressed, it display a menu of choices. It’s usually at the upper corner of the screen or window.
Why is it called a hamburger? Think of the top and bottom lines of as the bun with a patty in the middle. Now that you see it, it’s easier to say than “that thingy with the three lines.”
Functions identically to the vertical ellipsis menu button.