The assumption is that the person has lifted weights enough and had the genetic potential to actually add muscle. And anyway why would there be any discussion of “cut” or “bulk”, if there isn’t a foundation to work with.
Some areas to consider, but not all are necessary:
-
There should be obvious separation of the deltoid and triceps regardless of whether you pose or not…
-
The pecs should show obvious separation from the lower torso.
-
Abs are still vaguely visible when flexed, and obliques separation from the abs.
-
The front double biceps should show obvious biceps separation from the deltoid.
-
Upper back separation should show some separation and not be just smooth. Deltoids need to be distinct from the traps when back double biceps is posed. The traps begin to show separation from the rhomboids.
-
There should be enough quad separation to see both vastus muscles, plus a hint of the rectus femoris between the vastus muscles.
In other words, it is obvious to anyone that you lift weights. You don’t want to “bulk” until you can be confused with just being big, or a super heavyweight powerlifter. (220lb and lower weight classes in powerlifting don’t count as they just don’t “bulk” so far that they can’t make weight come competition.)
IMO, this is far superior to “measuring” percent body fat and making decisions based on your “measurement.” It can be highly flawed and misleading. Don’t chase a body fat number; strive for a look.