Gravitational acceleration g on Earth's surface is equivalent to an acceleration a = g in outer space.
a = g When the spacecraft engine is ignited and accelerating. The observer inside can not tell any difference from being on the Earth. Everything is falling down with an acceleration of g.
If the acceleration is more than g, it is called a high G. For example, 2g means that your weight is doubled.
If the acceleration is less than g, it is called a reduced g like on the surface of the Moon or Mar.
0 Gravity or weightlessness is inside a free falling elevator on the surface of the Earth.
The observer inside the elevator can not detect any weight.
Zero G is inside a spacecraft in outer space
without an engine thrust.