Yes, you are correct. The escape velocity typically refers to the minimum velocity required for an object to escape the gravitational pull of a celestial body (such as Earth) from a certain point above its surface.
When we talk about escape velocity, it's important to note that it is not measured at the surface of the celestial body but rather at a specific height above the surface. This is because, as you mentioned, rockets start with zero velocity at the surface and gradually accelerate to reach the necessary escape velocity.
The escape velocity can be calculated using the same formula:
Ve = sqrt((2GM)/R)
Where: Ve is the escape velocity, G is the gravitational constant, M is the mass of the celestial body, and R is the distance from the center of the celestial body to the point where the escape velocity is measured.
In practice, the escape velocity is often discussed in the context of escaping the gravitational pull of a celestial body from its surface, but it is technically applicable at any height above the surface where the velocity required to escape the gravitational field remains the same.