Pitch and Angle of Attack    
In simple terms: Pitch is the angle the wing appears to make with the ground and Angle of Attack (AoA) is the angle the wing makes to the airflow. The following diagrams illustrate pitch and AoA, and how deceptive the pitch of an aircraft can be to an observer on the ground.

Same AoA, different Pitch: Click to view figure 1.

Same Pitch, different AoA: Click to view figure 2.

PPG climb, cruise & glide descent: Click to view figure 3.

In fact under application of full power there is an increase in angle caused by the pilot being pushed ahead of the wing and so rotating the whole aircraft back. This results in a slower airspeed during climb. When the thrust is reduced to idle the wing enters a descending glide, the AoA returns to normal and the airspeed will return to full trim speed. In normal conditions with the correct size wing, the overall difference in AoA, power on/power off, is quite small and usually results in an airspeed variation of only 4 or 5 mph. This can be overcome on most modern PPG wings by the introduction of speed trimmers, allowing the pilot to mechanically decease the AoA by means of a leverage system in the risers by 3 or 4 degrees and so increase the airspeed, making a significant difference to how far you fly or how you progress against a headwind.

CofG: Centre of Gravity: The point of an aircraft at which it balances in all directions if it were rested on a pivot. In a PPG set up, as most of the weight is situated around the pilot, the CofG is typically a little way above the pilots head. It is this point, about which PPG will rotate when thrust is applied.