From Ubuntu11.04's help, it says: What is the meta key? The the meta key is key between the Ctrl and Alt keys on your keyboard. It may sometimes be called the windows key, logo key, system key, or even the Ubuntu key. If you have an Apple keyboard, there will not be a meta key on your keyboard. The Command (Cmd) key can be used instead. The meta key serves a special function in Unity. If you press the meta key, the Dash is displayed.
The main issue with the hoverboard is the battery. According to CNET, most hoverboards use lithium ion batteries, the kind often used in laptops and cell phones. But the liquid inside these batteries is flammable, and hoverboards (which have been produced and marketed out of thousands of essentially nameless factories in China) haven't adhered to a singular set of safety standards, and could very well be dangerous.
Lemon battery. A lemon battery is a simple battery often made for the purpose of education. Typically, a piece of zinc metal (such as a galvanized nail) and a piece of copper (such as a penny) are inserted into a lemon and connected by wires.