Intruder:
In common usage, "gradient" is represented in percent, while "angle" is represented in degrees. Take your pick as to which one you want to use, because they're essentially interchangeable.
In FAA-speak "gradient" is used for higher-than-standard climb gradients and is expressed in feet per mile. "Angle" is used for descent on approach procedures; the final approach segment.
Unlike PANS-OPs, TERPs does not use percentages to express required climb gradients.