A solution  is :
- A means of solving a problem or dealing with a difficult situation.
- The correct answer to a puzzle.
- Products or services designed to meet a particular need.
So by extension a business solution is composed of products  and/or services  addressing business needs  . Depending on the business context, business solutions are composed in variable proportions of products and services; sometimes only products, sometimes only services.
The ITIL® framework  defines “service”  a different way as “a means of delivering value to Customers by facilitating Outcomes Customers want to achieve without the ownership of specific Costs and Risks “. According to this definition the distinction between product and service as commonly understood by a non IT literate audience does no longer exist. Both definitions are valid depending on the context.
 solution, oxford dictionaries
 product, wikipedia
 product, merriam-webster
 service (economics), wikipedia
 service (economics) characteristics, wikipedia
 service (systems architecture), wikipedia
 service, oxford dictionaries
 service, ITIL® glossary of terms
 business, merriam-webster
 business, wikipedia
 business need, cambridge dictionaries online
 Business requirement, wikipedia
 ITIL® official website