All contributors except for Community Assistants and employees are volunteers. If you find an employee's profile, they will state they are an employee.
A volunteer is somone who does something on their own time and out of their own will, and a professional is someone who is very experienced in something. They are two completely different words....
"Explain" means to give additional information, such as details, rationales, or other clarification of an existing issue. It implies teaching, instruction, or the reiteration of knowledge.
"Discuss"...