What is escape velocity?

Throw a ball upwards and gravity brings it back. Throw it harder and it goes higher first. Escape velocity is the speed at which it never comes back at all — it keeps climbing, slowing forever but never quite stopping.

It depends only on the mass of the planet and how far from its centre you start. It does not depend on the mass of the thing escaping: a pebble and a spacecraft need exactly the same speed.

Rockets do not actually reach it in one throw. They climb steadily under continuous thrust instead, which is why the number matters more for the physics than for the flight plan. Reaching orbit needs far less — about 7.8 km per second.