n.1 a person who uses (esp. a particular commodity or service, or a computer).
2 colloq. a drug addict.
3 Law the continued use or enjoyment of a right etc.
Phrases and idioms:
right of user Law
1. a right to use.
2 a presumptive right arising from the user. user-friendly esp. Computing (of a machine or system) designed to be easy to use.