Services that require specialized skills, generally of high calibre and intelligence are known as professional services. It also normally requires a certificate, license, or registration process. As per a definition of a state legislative agency on the website:
Professional service refers to work offered by a free-lancer who has professional knowledge of the certain field of learning or science with its application to others affairs or practice of an art, but which is not confined to lawyers, certified registered nurse, dentists, psychologists, anesthetists, veterinarians, engineers, architects, land surveyors, accountants, claims adjusters and landscape architects.
A profession refers to a vocation based upon specialized and lengthy intellectual training that helps in rendering a particular service. The word “professional” refers to professed achievements in a certain field different from mere skills.