What are FS, FF, SS, SF dependencies?

FS, FF, SS, SF — are types of dependencies between tasks in project management, which describe the order and logic of work execution:

• FS (Finish to Start) — task B cannot start until task A is completed. The most common type of dependency.
• FF (Finish to Finish) — task B cannot finish until task A is finished.
• SS (Start to Start) — task B cannot start until task A starts.
• SF (Start to Finish) — task B cannot finish until task A starts (rare dependency type).

Example: if you need to first build the foundation (A), and then start constructing the walls (B), this is an FS dependency: the walls start after the foundation is finished.