Bobbysgirl19 I expect that was what Marthabeck meant, but in case she doesn't answer - it is usual, when members of an organisation are voting to make a big change in the constitution, for it to be specified that more than a certain proportion of all those eligible to vote must vote positively for the change, for it to be passed. The proportion is usually far more than a simple just-over-half of those who did vote.
So, for instance, if only a third of all who could have voted were for a change a third voted against it and a third didn't vote at all, it would not be passed.
In this referendum, about a third of those who could have voted for a change in the constitution of the whole country ^ wanted to leave, the other two-thirds either didn't want to or didn't vote.