The point in a rocket’s ascent when aerodynamic pressure is greatest is called Max Q.
The term is short for “maximum dynamic pressure.” Dynamic pressure depends on air density and the square of a vehicle’s speed. Near the ground, air is dense but the rocket is moving relatively slowly; higher up, the rocket is faster but the atmosphere is thinner. The maximum occurs between those extremes.
Rocket designers pay close attention to Max Q because aerodynamic forces and structural loads are especially significant there. Many launch vehicles deliberately reduce engine power, a procedure often called throttling down, as they approach this point. They increase power again after passing through it.
Max Q is not the same as maximum speed, maximum altitude, or escape velocity. It is a loading condition caused by the interaction between speed and atmosphere. The exact altitude and time vary with the rocket’s design and flight path.