The term "final user" refers to the person or entity who ultimately uses a product or service. There are several synonyms for this term, including end-user, consumer, customer, and client. Each of these terms is used in different contexts, but all refer to the same basic idea.
End-user is a commonly used synonym for final user, and refers to the person who uses a product or service after it has been manufactured or developed. Consumer and customer tend to be used more in the retail industry, as they refer to individuals or entities who purchase goods or services. Client is often used in the service industry, specifically referring to individuals or organizations who contract with a business for various services. Regardless of the context, all of these synonyms refer to the ultimate recipient or user of a product or service.