Checks and balances and separation of powers are two of the most important aspects of the American governmental system. Both of these are meant to ensure that no one part of the government can become too strong and, potentially, abuse the rights of the people.
Separation of powers means that the different powers of government are divided up and given to separate branches of government. For example, the legislature makes the laws, but it cannot enforce them. Instead, the executive branch has to enforce them. The executive branch gets to enforce the laws, but cannot actually make them. This means that no branch of government has all the power.
The term “checks and balances” refers to the fact that each of the branches of government has some degree of power in the others’ areas. For example, we know that the main function of the legislative branch is to make laws. However, the legislature does not have complete control over this. Instead, the president (head of the executive branch) can veto laws that he (or someday she) does not like. By giving each branch some power over the others, we make it harder for any one branch to abuse us. If, for example, Congress passes laws that would hurt the people, the president can veto them. Thus, checks and balances and separation of powers are ways to limit the power of government so it cannot hurt the people very easily.
"Checks and Balances" and "Separation of Power" can also be applied to other forms of government, too. For example, successful corporations and nonprofits use these techniques to govern business practices to ensure business is performed in an ethical manner to discourage embezzlement, racketeering etc.