A presidential system of government is a government in which a president leads an executive branch that is separate from the legislative branch. The United States is a good example of a presidential system of government.
There is no guarantee that a president in a presidential system of government will have any control over the legislative branch; in the United States, the president does not have the power to make or dismiss legislation. A president has the power to take charge of certain legislation he or she wants to see passed. Compared to a parliamentary-type government, the president has more power in this respect. Bills and laws waiting to be passed can be blocked by either the President, the Supreme Court or Congress and there is nothing the President can do about it.
In a presidential system of government, the executive branch is isolated and unlike a parliamentary system, the president and his or her cabinet come from different backgrounds and may not always have the same goals in mind. The parties in this type of government are typically less organized than a parliamentary government and while the power in a parliamentary government is spread between the Prime Minister and his or her ministers, the power and responsibility in a presidential system of government sit squarely on the shoulders of the president.