Comprehensive and Detailed Explanation From Exact Extract:

A Service Level Indicator (SLI) is a measurement of some aspect of reliability (e.g., latency, availability, quality). One of its defining characteristics is that it must be measured over a specific time window. Without a time horizon, the SLI has no actionable meaning.

From the Site Reliability Engineering Book, Chapter “Service Level Indicators”:

“An SLI is a quantitative measure of some aspect of the level of service that is provided. SLIs are evaluated over a specific period of time in order to understand reliability as experienced by the user.”

The SRE Workbook further states:

“Every SLI must define a measurement window. Without a time horizon, the indicator cannot be used to calculate SLO compliance.”

Why the other options are incorrect:

A SLIs do not need to appear in an SLA; SLAs are external contracts, SLOs/SLIs are internal engineering tools.

B SLIs may include client-side, server-side, or network metrics depending on what reflects user experience.

D SLI agreement is not defined by SRE vs. Agile teams; it is defined by business and user need.

Thus, the correct answer is C.