Point of view is all about staying inside the mind of a specific character. This means that all descriptions, vocabulary, speech, and level of understanding should be within the scope of what that person knows.

For example, if your protagonist or other POV character is a teenager or child, they are going to see the world through that filter. Thus their comprehension and word choice should be appropriate for someone of that age. The came principle goes for an adult who is deemed highly intelligent. They will see the world according to their assumed education and experience and use more sophisticated speech patterns.