In performance measurement for interactive systems, the elapsed time from submitting a query until the first useful response is received is called what?

Introduction / Context:
Understanding performance metrics helps tune systems and set service-level objectives. For interactive workloads (queries, API calls), the key user-perceived metric is how quickly the system answers.

Given Data / Assumptions:

• An interactive user submits a request.
• We measure elapsed time until the first useful output is returned.
• We must choose the correct term.

Concept / Approach:
Response time includes queueing, processing, and communication delays from request initiation to initial response. Turnaround time usually applies to batch jobs from submission to completion. Waiting time is the queueing portion only; processing time is CPU/IO service time excluding waits.

Step-by-Step Solution:

Verification / Alternative check:
Performance engineering literature consistently defines response time as end-to-end elapsed time for interactive requests.

Why Other Options Are Wrong:
Batch turnaround differs; waiting and processing are partial components, not the total.

Common Pitfalls:
Optimizing CPU time alone without reducing queuing or network latency fails to improve perceived response time.

Final Answer:
Response time