Falsifiability is a principle in science that states a hypothesis or theory must be testable and able to be proven false. This means that there should be a possible observation or experiment that could show the idea is incorrect. For example, if someone claims that all swans are white, this can be tested by looking for a non-white swan. The concept of falsifiability was popularized by philosopher Karl Popper, who argued that scientific theories should be structured in a way that allows for potential refutation. This distinguishes scientific claims from those that are untestable, such as personal beliefs or opinions, which cannot be proven wrong.