Takeoff Clearance: The Magic Words

The takeoff clearance is the instruction you have been waiting for. When the tower is certain the runway is clear, that wake turbulence is no longer a factor, and that no other traffic will conflict with your departure, they will give you the takeoff clearance.

A takeoff clearance in the standard format contains:

Wind (if not already given in the line-up instruction)
Runway number
"Cleared for takeoff" or "Take-off free" (German equivalent: "frei")

The word "cleared" or "free" is what makes this a takeoff clearance. You are now authorized to apply takeoff power and depart the runway.

You must read back the entire clearance:

Wind (if given)
Runway number
The word "cleared for takeoff" or "free" (do not say "takeoff approved" or "approved for takeoff"—those are different)