Compulsory voting
Compulsory voting is an effect of laws which require eligible citizens to register and vote in elections, and may impose penalties on those who fail to do so. , 22 countries provide for compulsory voting, and 11 democracies — about 5% of all United Nations members — enforce it.
Donkey vote
In systems where voting is not compulsory, it seems counter-intuitive that many who attend the polls would be apathetic. However, there may be countervailing factors that produce a "donkey vote" even with voluntary turnout. In many US elections, a voter may well be intensely interested in (e.g.) the Presidential contest but not in other, less prominent races on the same "long ballot".