A mobile device (or handheld computer), also referred to as a digital assistant (or DA), is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical keyboard. Many mobile devices can connect to the Internet and connect with other devices, such as car entertainment systems or headsets, via Wi-Fi, Bluetooth, cellular networks, or near-field communication. Integrated cameras, the ability to place and receive voice and video telephone calls, video games, and Global Positioning System (GPS) capabilities are common. Power is typically provided by a lithium-ion battery. Mobile devices may run mobile operating systems that allow third-party applications to be installed and run.