This is a built-in turtle variable. It indicates the direction the turtle is facing. This is a number greater than or equal to 0 and less than 360. 0 is north, 90 is east, and so on. You can set this variable to make a turtle turn.
Example:
set heading 45 ;; turtle is now facing northeast set heading heading + 10 ;; same effect as "rt 10"
Take me to the full NetLogo Dictionary