Service Level Management is design process that helps build a relationship with the business, that looks to put IT on more than a Master to Slave relationship. 

It is made up of a number of aspects

Service Level Agreements - this is an agreement between the the Business and IT on what levels of service IT will provide. Naturally with unlimited money IT could likely provide 100% of availability of all systems or very close to it. But money and resource are factors so often there are propsoed service teirs, if you want more availabilty for example then you may a higher rate.

Operational Level Agreements - Oparational agreements are often betwen an IT Customer Service department and the technical teams, setting out the leveld of service that will be needed to meet the service level agreemenmt. Often this is a chicken and egg thing, 

Vendor Contracts

Alignment with Service Catalogue