What is the anaerobic threshold?

As the intensity of aerobic exercise increase, there comes a point or threshold where the aerobic systems can’t furnish the energy needed at the higher intensities. Fortunately, inside the muscles fibers, energy can be made anaerobically to make up for what the aerobic system can’t supply.

[rhidiandavies]

Isn't this aerobic threshold? As I understood it, anaerobic threshold is the point at which your blood lactate level ceases to increase linearly with effort?