Lets you delete tasks. Use done if you finish a task, use this if you accidentally created a task you don't want.
You can also use delete /search terms to save a step in deleting multiple tasks. If the search returns multiple tasks, then it'll ask for confirmation so you don't accidentally delete unrelated tasks. Just say y to delete all the tasks; anything else is interpreted as a fresh command.
See also help context if you're wondering how the last example works!
Examples: