Final answer:
In project management, Task B not being able to start until Task A is completed is known as a Finish to Start (FS) dependency, which is critical for managing the project timeline.
Step-by-step explanation:
When a project manager is identifying task dependencies and finds that Task B cannot start until Task A is complete, this situation represents a Finish to Start (FS) dependency. This is the most common type of dependency in project management. In a Finish to Start relationship, the start of the successor task (in this case, Task B) depends on the completion of its predecessor task (Task A). It's essential for creating a logical sequence of tasks and managing the project timeline effectively.