Who is Amazon merchant?

Could you please clarify for me what exactly an Amazon merchant is? Is it an individual or a business that sells products on the Amazon platform? And how does one become an Amazon merchant? Do they need to meet certain criteria or go through a specific process? Additionally, what are the benefits and drawbacks of being an Amazon merchant? I'm particularly interested in understanding the financial aspect of it, such as the fees and commissions associated with selling on Amazon, as well as the potential for profit margins and growth opportunities.