What is Latency? — UK Software Development Guide
Direct Answer
Latency is the time delay between a request being made and the response being received. In software, API latency is typically measured as p50 (median), p95 (95th percentile), and p99 (99th percentile) response times. Low latency means fast responses; high latency means slow responses. Latency is distinct from throughput (how many requests per second a system can handle).
Latency in the UK
Latency has UK regulatory significance. FCA operational resilience (PS21/3) requires FinTechs to define impact tolerances for important business services — typically expressed as maximum acceptable response time under load. NHS DSPT Standard 10 expects acceptable performance under NHS clinical workloads. For UK eCommerce: Akamai and Google research shows every 100ms of additional latency reduces conversion rate by approximately 1% — making latency directly revenue-relevant for UK online retailers. ClickMasters targets p95 < 200ms for most UK API endpoints.
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