What is the difference between flow separation and turbulent flow?
At what point does one say &quot;oh, this flow has changed from turbulence to separation&quot;

At the point where the flow reverses direction.

Flow separation. The bold curve is the surface/wing.
Yes, that can happen.
Both turbulent and laminar flow can separate. Turbulent flow is in fact less likely to separate than laminar flow. This is why aircraft wings often have devices that deliberately create turbulence on the wing.
(Yes, separated flow produces negative skin friction, but at the price of huge pressure drag)
Here's a (badly hand-drawn) diagram showing the difference between laminar, turbulent and separated flows.

Just a clarification about stall. The stall is when the lift reduction caused by flow separation overwhelms the lift increase caused by flying at an increased angle of attack. Flow separation can happen without stall, and it will reduce the benefit gained from a higher angle of attack in proportion to the extent to which the flow is separated, but stall cannot happen without flow separation.
Indeed, many wings have separated flow at the trailing edge sometime before &quot;stall&quot; is reached. As one draws closer to &quot;stall&quot;, the region of separated flow expands forward. The turbulence created by the wake of this separated flow hits the tail, causing &quot;buffeting&quot;, which gives the pilot a warning that he is approaching stall. Airfoils that lack this feature, such as supercritical airfoils or sharp supersonic ones, tend to be dangerous to fly at slow speed with it's inherent high angles of attack.
And as you can see from the diagram, the flow separation at a given angle of attack is much worse for laminar flow than for turbulent flow. So the laminar separated case is more likely to be a stall than the turbulent separated case.

Lift vs angle of attack for thin, sharp wings vs thick ones. Airfoils designed for laminar flow fall in the thin category. And as above, just having or not having laminar flow on a wing can make a similar difference.
And yes, vortex generators prevent separation by creating turbulence, which causes high speed freestream air to get mixed with low-speed boundary layer, speeding up the boundary layer. It's a tradeoff between the drag of a turbulent boundary layer and the even greater drag and lift loss from flow separation.