Consumer Lag
The distance between a consumer's processed position and the current end of a stream, exposing accumulated work when production outpaces sustained consumption.
Consumer lag answers how far a consumer is behind in stream position, not necessarily how old the oldest pending message is. At high traffic, a short time delay may represent many offsets; at low traffic, a small offset gap can still contain an old record.
Lag is therefore more useful when read with arrival and processing rates. If production persistently exceeds consumption capacity, the system has an unstable queue rather than a temporary backlog. Related examples appear in distributed data-system concurrency and ASR queue stability.