Actually, both of those examples would fit the definition JD posted.
The difference is that what you are given by "Clearance delivery" may or may not match exactly the route you requested when you filed your flight plan. You'll sometimes hear, "(yada,yada, yada, up to a certain point in the route), then as filed..."
In that case, essentially they're saying, "you're *not* authorized to follow the route you filed for, but you *are* authorized to follow this one..."
Once that business has been taken care of, you can get on with the other "clearances", like the one for takeoff.
The essence of it is that the pilot is in command of the flight--ATC cannot tell the pilot what to do, only tell him what he is *authorized* to do. "Cleared for takeoff" doesn't mean the pilot *must* take off, only that he is now authorized to do so. Similarly, "cleared to land" doesn't mean that the pilot must land, only that ATC says it's ok for him to do so.
(Although if they're busy and you don't do what they've cleared you to do, when they want you to, they get really annoyed.)
On the other hand, if the pilot does something he's *not* cleared to do, like flying faster than cleared to, or at a different altitude or heading, then there'd *better* be a life or death reason for it....
