However, a user's privilege may further constrain the domain of accessibility of other users' terminals. Other address formats and how they are handled are unspecified. If the recipient is logged in more than once, terminal can be used to indicate the appropriate terminal name. If terminal is not specified, the talk message will be displayed on one or more accessible terminals in use by the reci- pient. The format of terminal will be the same as that returned by who.
TERM Determine the name of the invoker's terminal type.
If this variable is unset or null, an unspecified terminal type will be used. An error occurred or talk was invoked on a terminal incapable of supporting it. For example, some implementations provide line editing functions with certain control character sequences.