What type of dependency indicates that two activities can only start at the same time?

The concept being addressed in the question revolves around the relationship between tasks in a project schedule. A dependency that indicates two activities must start simultaneously is termed a Start-to-Start dependency.

In a Start-to-Start relationship, the initiation of one activity directly impacts the initiation of another. This means that as soon as the first task begins, the second task must also commence at that same moment. This type of dependency is crucial for projects where tasks are interlinked and need to proceed in parallel to optimize resource utilization or meet specific timelines. For instance, if two team members are required to work together on a portion of the project, they must both start their tasks concurrently to ensure collaborative progress.

The other types of dependencies illustrate different relationships: Finish-to-Finish involves the completion timing between tasks; Start-to-Finish indicates that one task cannot finish until another starts; and Finish-to-Start is a typical dependency where one task must finish before another can begin. These types do not encapsulate the idea of simultaneous starting, which is why the Start-to-Start dependency is the appropriate choice here.