A parliamentary democracy is a form of government where voters elect the parliament, which then forms the government. The party with the most votes picks the leader of the government. Prime ministers are beholden both to the people and the parliament.
After the prime minister is chosen by the parliament, the prime minister then picks members of the parliament to form his cabinet. The parliament is determined by a democratic vote in the general election. Laws are drafted and passed by both the prime minister and the parliament. As the prime minister remains a member of parliament, he or she can personally draft legislature and put it up for a vote.
The minority party's duty is to challenge the majority whenever necessary. If the majority party loses power, the prime minister is removed from his or her position. The prime minister can even be removed with a vote of "no confidence" by the parliament.
Parliamentary democracy originated in Britain and is still used there today. Many of its former colonies have adopted parliamentary democracy or some form of it. Even though these countries function as a democracy, they can still be constitutional monarchies, with a king and queen, such as the United Kingdom.