A Service-Level What?
For any given service—be it provided by software (e.g., application, platform), hardware (e.g., infrastructure), or human (e.g, delivery, support, documentation)—there is a level of reliability required to achieve user satisfaction. While users, from end users of web or mobile applications to developers that use a platform, want to utilize a service's features, they care more about service reliability. After all, if the service is not working, they cannot make use of those features.