During Direct Path write operations the data is asynchronously written to the database files. At some point the session needs to ensure that all outstanding asynchronous I/O have been completed to disk. On UNIX the fsync command, which synchronizes data to disk, is issued to confirm that all the writes have completed and the data is all on disk.
Wait Time: The time taken for the fsync operation to complete, which normally is the time taken to complete the outstanding I/Os.