The Workflow activity "Wait For Concurrent Program" waits for the concurrent program to be complete before proceeding with the other actions, Internally the flow is like below:
The activity uses PLSQL pakcage fnd_wf_standard.Seed_CB to verify if the program is complete and waits for average program time and then checks if the program is complete. If complete it returns a value to continue with the workflow. If the program is not complete and not running then it seeds concurrent request post processor actions (FND_CONC_PP_ACTIONS) to notify the workflow back when the program is complete. The concurrent post processor complete post processor action i.e FND_WF_STANDARD.callback to notify the workflow and to continue further.
