Service quality management covers all measures by which a buyer defines, secures and improves the quality of externally sourced services.
The buyer's perspective. The term is mostly used from the provider's side. In procurement the buyer's view counts: how does the buyer make sure the purchased service has the agreed quality?
Building blocks. Quality requirements in the scope of work and statement of work, acceptance criteria, ongoing measurement, stakeholder feedback, corrective actions, and feeding lessons back into the next tender.
How intensive. Studies on purchased services name intensity of use, risk of quality failures, degree of standardisation and volume as factors that shape how intensively quality is managed. In practice: spend the effort where a defect is expensive.
Where it sits. Service quality management is the overall frame. Performance measurement supplies the numbers, quality monitoring observes continuously, service provider evaluation condenses the judgement.