Service management is a set of specialized organizational capabilities for enabling value for customers in the form of services. These capabilities include tangible things like capital, people, and equipment, and can also include intangible things like knowledge, management and skills. These capabilities can also include intangible things, like knowledge, management, and skills.
https://www.bmc.com/blogs/itil-key-concepts-service-management/#:~:text=Service%20management%20is%20a%20set,like%20knowledge%2C%20management%20and%20skills.

A change is defined as the addition, modification, or removal of anything that could have a direct or indirect effect on services
https://www.bmc.com/blogs/itil-change-enablement/#:~:text=A%20change%20is%20defined%20as,or%20indirect%20effect%20on%20services.