A floodgate is a barrier or gate that is designed to be opened and closed in order to control the flow of water. It can refer specifically to a large, heavy gate that is used to close off an area from rising waters during a flood, or it can also refer more generally to any situation where one event leads to a chain reaction of similar events. The term "floodgate" is often used metaphorically to describe a situation in which something small and seemingly insignificant has unintended consequences that lead to much larger problems.