What did James Madison mean when he describes the need for safeguards from the tyranny of the majority?

Under the British system, with no written constitution, any law written by the majority is automatically in force. This could include (and did under British conditions) making a particular person a criminal by legislative fiat. Majorities could in the rush of emotion pass all sorts of weird legislation. Madison made sure that if this came close to happening in the USA, courts could stop it, and hopefully the bicameral nature of Congress might also.