does anyone know what a g is?

Are you talking about when someone says that astronauts experience several g's when taking off from the launch pad?

A g represents the amount of force exerted by the Earth's gravity on an object at sea level. So, to experience several g's means that you are feeling several times the normal force of gravity. You can feel that a little bit when you go up in a fast elevator, for example. When astronauts take off in the shuttle, they have to be going a LOT faster than your elevator, however, so they will experience many more g's than normal.

I've linked to a short, somewhat technical, definition below:

"Gravitational acceleration (symbolized g) is an expression used in physics to indicate the intensity of a gravitational field."

A "g" or "A G"?

A. G. = Attorney General

a gangster