Weightlessness is the complete or near-complete absence of the sensation of weight. This is also termed zero-G, although the more correct term is "zero G-force". It occurs in the absence of any contact forces upon objects including the human body.

Here a video with an experiment which shows why the astronauts in ISS feel no weight , although the gravity is still there in the hight from about 400 km.

I plan to add a translation next days