The "restart" command is used to start a new session without exiting and re-launching the program. "restart" completely erases all defined session objects such as variables (even "lock"ed ones), equations, and recognized noun phrases from Converse mode.
It also disregards any unanswered questions and will close an open log file.
Note: "restart" does not reset run-time options, so any changes made via the "set" command will remain in effect.