What do we call a period when no productive work is occurring?

The term that accurately identifies a period when no productive work is occurring is commonly referred to as "Idle Time." Idle time specifically denotes intervals during which workers or machinery are unable to engage in productive activities, often due to factors such as lack of materials, machine breakdowns, or inefficiencies in workflow.

While "Downtime" is related and refers broadly to periods when operations are halted, it isn't exclusively tied to lost productive work time, making it a less precise term for describing no productivity. "Lead Time" relates to the duration taken from the initiation to the completion of a process, and "Off-Peak Time" typically describes periods when demand for a service is lower but does not directly correlate to productive work being halted or absent. Thus, "Idle Time" is the correct designation for when no productive work is happening.