Mobile computing is human–computer interaction by which a computer is expected to be transported during normal usage. Mobile computing involves mobile communication, mobile hardware, and mobile software. Communication issues include ad hoc and infrastructure networks as well as communication properties, protocols, data formats and concrete technologies. Hardware includes mobile devices or device components. Mobile software deals with the characteristics and requirements of mobile applications.
Mobile Computing is "taking a computer and all necessary files and software out into the field and the system". There are several different dimensions under which mobile computers can be defined: (1) in terms of physical dimensions; (2) in terms of how devices may be hosted; (3) in terms of when the mobility occurs; (4) in terms of how devices are networked; (5) in terms of the type of computing that is performed. 
In terms of dimensions, mobile computers tend to be planar and tend to range in size from centimeters to decimeters. Mobile computer may themselves be mobile, e.g., it is embedded into a Robot or Vehicle that is mobile or itself may not be mobile, but is carried by a mobile host, e.g., the mobile phone is not mobile but it is carried by a mobile human. The most flexible mobile computer is one that can move during its operation or user session but this depends in part on the range of any wireless network it is connected to. A tablet or laptopcomputer connected via Wi-Fi can move while staying connected within the range of its WLAN transmitter. To move between multiple different located WLANs, the device must interrupt, suspend, or close its current user session before connecting to another WLAN transmitter in another session. A device such as a tablet or mobile phone can move much further while staying connected within the range of a GSM network as it can seamlessly move between multiple GSM transmitters or Base stations. Mobile computers may also support or form part of a more local network that moves as the devices, i.e., mobile computers may also be used as part of a Wireless Body Area Network, Wireless Personal Area Network or a piconet. Depending on the type of application the mobile computer runs, the computation of the applications may run only locally, e.g., a PC game. The majority of mobile computers for personal use tends to be used for communication or for remote data downloads such as remote Web access (see Mobile Internet device). As some mobile computers contain an array of sensors, microphones and cameras, these can be used for local data capture, filtering tagging and remote uploads. Increasing mobile computers are also being used to access services such as travel, payment or for access to controlled physical spaces.
see more: https://en.wikipedia.org/wiki/Mobile_computing