What are some of the similarities and differences between a parliamentary and presidential democracy?

Parliamentary systems and presidential
systems are both forms of representative government, which are run through elections (by which
citizens select representatives to represent them). Additionally, they both tend to involve the
use of political parties, which tend to play a critical role in shaping the practical realities
of each political system.

However, while both presidential and parliamentary
governments might be representative in nature, there are critical differences between the two
systems. Perhaps most importantly, you should be careful not conflate the office of the prime
minister and the president. A president is the head of the executive branch and is selected by
its own electoral process. A prime minister, on the other hand, is the party leader for
whichever party holds power in the legislature at any time. When elections are held, a new prime
minister is selected if a new party gains political ascendancy within parliament. From that
perspective, the clear distinction between the executive and legislative branches, which exists
and defines presidential democracy, does not exist under a parliamentary
system.