background worker
A part of the back end that runs jobs on its own, away from the requests users make.
A background worker is a process or task that consumes work (messages, scheduled jobs) independently of the request/response path, so slow work never blocks an API call.
Examples
Sending an alert email or rebuilding a day of hourly averages runs in a background worker, so neither an HTTP request nor the next reading at the broker waits behind it.
See also