Being dependent means relying on something. Many people are dependent on coffee in the morning, while a dependent is someone who relies on you for financial support. In grammar-land, a dependent clause can’t stand alone because it’s a fragment.
Dependent comes from pendant, the French word for "hanging.” If you break your leg, you will be dependent, or hanging, on crutches to get around. Kids are dependents of their parents, since they rely on them for food and shelter. A drug addict is dependent on drugs. And if a decision is dependent on your mood, that means it depends on or will be decided by how you feel.