Work waits for resources
A task can be ready but unable to proceed because the required person, machine, room, approval or information is busy. That time is a queue. Queues are common in both business processes and personal schedules.
When capacity is tightly loaded, small variations can create disproportionately long waits. Leaving some headroom or smoothing arrivals can improve reliability even when raw work speed does not change.
Name the reason for the wait
Separate external waiting, internal approval, material availability and scheduling delay. Different causes need different solutions. A faster worker cannot solve a supplier lead time, while a better handoff may reduce an internal queue.
If waiting is expected and fixed, include it directly. If it is variable, record a range or use historical data rather than hiding it in unexplained padding.