The search term “sound panels” is another example of how people take things they are familiar with and put them together to try and communicate something. Unfortunately, this process only confuses the issues.
I think people use the term sound panel or sound panels to mean a structure that reacts to sound in some way. My best guess is that sound panel means some sort of panel or structure that does something for or to sound. To an engineer, it means a panel that produces sound energy. I think to most people it means a panel that absorbs sound because their environments they are in are too noisy.
Sound panels could be a panel with speakers in it as is used in sound reinforcement venues such as concerts. A PA or public address system could be referred to as a sound panel. An electrostatic speaker could be a sound panel. An electrostatic speaker is a panel type structure that produces sound energy through a vibrating membrane constructed of screen wire which an electrical current is passed through.