In engineering, especially military, a portable device or system is a mobile piece of equipment that is small enough to be carried, and used "on the move", by a single person. It has a self-contained, or replaceable battery power system.
Portable devices may be used in the hand, such as a cell phone, which come in a variety of standard form factors or shapes. They may also, as with a larger military radio such as the AN/PRC-117, be packaged as a backpack. There are civilian applications in which a portable device is packaged in a customized briefcase or other piece of hand-carried luggage.
AN- designations for portable military electronics begin with the letter "P".
Portable computers range from laptops to notebooks to palmtops. "Wearable" computers in clothing or goggles generally meet the definition of portable.