'“The total span of working time or elapsed time required to complete a task. When applied to summary tasks, it represents the amount of time between the start of the earliest subtask and the completion on the latest subtask. Duration can also be displayed at project level against a project summary task. Durations against tasks can be estimated or confirmed. If the task has assignments against it, the task's duration may be calculated according to the scheduling formula.

'SOURCE; projectlearning.net

1. 'The number of work units (not including holidays or other non-working periods) required to complete an activity or other project element. Usually expressed as work days or work weeks.2. 'Elapsed time.

SOURCE: apm.com

Duration is the length of time needed to complete an activity.

SOURCE: welcom.com”