Flux, a query language used for InfluxDB, requires a time range when querying the database. This is done using the `range()` function, which takes two parameters: `start` and `stop`, defining an absolute or relative time range. Relative time ranges are defined using durations relative to "now", while absolute time ranges use timestamps in ISO format. The `range()` function includes points that match the start time but excludes those that match the stop time.