An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."
A Useragent is software (a software agent) that is acting on behalf of a user. For example, an email reader is a mail user agent. In the Session Initiation Protocol (SIP), the term user agent refers to both end points of a communications session.