What are the IO Waits Breakdown metrics in the SQL Server IO Activity Report based on? (4382937)

What do the I/O Data Page, I/O Completion, and I/O Bulk Load metrics in the SQL Server I/O Activity Report represent?

• I/O Data Page: Foglight's label for waits spent waiting on physical I/O for data pages (this maps to SQL Server page I/O waits such as PAGEIOLATCH_*).
  • Metric: DBSS_Wait_Io_Data_Page_Rate.
• I/O Completion: Foglight's label for waits on asynchronous I/O completion (this maps to SQL Server I/O completion waits such as ASYNC_IO_COMPLETION / IO_COMPLETION).
  • Metric: DBSS_Wait_Io_Completion_Rate.
• I/O Bulk Load: Foglight's label for bulk-load related I/O waits (large sequential I/O caused by bulk inserts/ETL; the SQL Server bucket name can vary). 
  • Metric: DBSS_Wait_Io_Bulk_Load_Rate.

• I/O Data Page: slow storage (latency), excessive physical reads due to scans, missing indexes, or small buffer pool.
• I/O Completion: high asynchronous I/O latency, blocked threads waiting on I/O completion, or overloaded I/O stack.
• I/O Bulk Load: heavy bulk/ETL operations producing sustained high sequential I/O and queueing.