Final answer:
An ad populum fallacy is an appeal to widespread beliefs of people, stating that a proposition is true because many people believe it, which can be misleading as popularity does not guarantee truthfulness.
Step-by-step explanation:
An ad populum fallacy is an appeal to widespread beliefs of people. This kind of fallacy occurs when it's argued that a proposition is true because many or most people believe it. Essentially, the ad populum fallacy is suggesting that if something is popular or widely accepted, it must be true or acceptable. The bandwagon fallacy, a subtype of ad populum, specifically suggests that one should do or believe something because many other people do so.
However, the popularity of belief does not necessarily correlate to its truthfulness. Critical thinking and evidence are necessary to validate claims rather than relying on the sheer number of people who hold a certain belief. This is important to remember in a range of situations, from everyday decisions to evaluating advertising claims, which may use the ad populum appeal to convince consumers to align with the majority and purchase a product.