The fallacy of appeal to popularity (or argumentum ad populum, also bandwagon) occurs when an arguer uses the popularity of an opinion or view to determine whether the claim is good or bad, false or true. This may involve its popularity in general, or with respect to a certain group.

Here is an example:

"Because most Italian coach builders prefer to put Recaro seats in their sports cars, no other seat really belongs in a sports car."

The problem here is that Recaro's being the most popular seat in a certain class of cars (Italian sports cars) is no guarantee that it is the best, or that "no other seat" is suitable for such cars.

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