A reference letter is a general endorsement or commendation of a person that confirms the required abilities or stated facts. It also proves that the writer knows you personally and can verify certain facts about you and your performance. Generally stands alone as a show of approval to be used as needed.
A recommendation letter highlights or emphasizes skills, knowledge, and experiences that qualify the candidate for a specific opportunity. Such as a particular role within a company or a specific scholarship, program, etc. Hence the skills and experiences verified or referenced will pertain to the requirements of the company or organization.