Drought is a period of unexpectedly long dry weather. Deserts do not have droughts because everyone knows rain is unreliable. In some parts of the world there is a season of the year with rain and a season without. The dry part of the year is not usually a drought because everyone knows this is what it will be like.
However, some years the rains 'fail'. Then there is a drought. If a region depends on rain for its crops and that rain is too small, then the crops will not grow and people may starve.
