Suppose you have a box that is a cubic meter. It is made of copper. It is solid. It has 1000000 extra electrons. It has an overall charge of 1000000 electrons that are spread all over it's volume.
It means the excess or deficiency of the number of electrons on a body capable taking on or giving up electrons. When the electrons are taken on or given up, there is no chemical change.
I usually try and answer this kind of question by an example because I don't think the definition is always clear on it's own.