usage

The way in which statements in a command or programming language are actually used. In geoprocessing, usage for a tool or environment setting can be viewed at the command line.

usage time

[Internet] The amount of time between when a client gets a reference to a service and when they release it.

user interface

[software] The aspects of a computer system or program with which a software user can interact, and the commands and mechanisms used to control its operation and input data.

user name

[programming] The identification used for authentication when a user logs in to a program.