What do Gs stand for in space flight?
Gs stand for gravities.
Einstein said that gravity and acceleration are indistinguishable. So, if you accelerate at 9.81 m/s/s you would experience the same force as standing on the Earth's surface.
If you accelerate at 19.62 m/s/s you are experiencing twice the force of gravity or 2G. Space rockets need to accelerate rapidly to overcome the Earth's gravity. The acceleration is often measured in terms of multiples of Earth's surface gravity or Gs.