A more thorough explanation:

The ordinary-observer test is a legal standard used to determine whether a particular work infringes on another's copyright. It asks whether an ordinary person, with no specialized knowledge of the subject matter, would find the two works substantially similar.

For example, if a musician creates a song that sounds very similar to another song that was previously released, a court might use the ordinary-observer test to determine whether the new song infringes on the copyright of the original song. The court would ask whether an ordinary person, without any musical training or expertise, would find the two songs substantially similar.

Another example might be if a company creates a logo that looks very similar to another company's logo. The court would use the ordinary-observer test to determine whether an ordinary person, with no knowledge of graphic design or branding, would find the two logos substantially similar.

The ordinary-observer test is important because it helps ensure that copyright law protects original works without stifling creativity or innovation. By using a standard that is based on the perspective of an ordinary person, rather than an expert, the law can more accurately reflect the views and opinions of the general public.