In aerodynamics, angle of climb is the ratio between distance travelled over the ground and altitude gained. The angle of climb can be expressed as the angle between a plane horizontal to the Earth's surface and the actual flight path followed by the aircraft during its ascent. See remarks on the notations used for best angle of climb speed Vx in the article on rate of climb.
This v-speed is the one a pilot uses when executing a "short field" takeoff, because it gains the most altitude in a given distance. Rate of climb is not a critical factor, for the best angle of climb speed may in fact be slower than the best rate of climb speed, and clearing an obstacle is not something that is time dependent.
Best angle of climb (BAOC) airspeed for an airplane is the speed at which the maximum excess thrust is available. Excess thrust is the difference between the total drag of the aircraft, and the thrust output of the powerplant. For a jet aircraft, this speed is very close to the speed at which the total minimum drag occurs.