External antennas are a type of an antenna typically used outside a device. This can be terminal mount antennas used indoors on devices such as routers, or rugged IP67 rated antennas that can be used on the roof of a vehicle in harsh environments and weather conditions.
There are three main types of external antennas: omnidirectional, directional and high-gain. Omni-directional antennas are used for general reception in all directions. Directional antennas have less gain than omnidirectional ones, but they can be focused in a specific direction. High-gain antennas have more gain than both omnidirectional and directional ones, but their reception area is smaller.
External antennas are often used to extend the range of a wireless network. If there is not enough signal strength from the router or access point, an external antenna may help boost this signal for better connectivity.