AWR IO Stat "Av Buf Wt(ms)" definition and meaning

I got conflict response when I try to find what is the definition of "Av Buf Wt(ms)" in IO Stat section of AWR report.

One opinion says it is "average buffer writes in milliseconds", other opinion says it is "average buffer waits in milliseconds". I am wodnering where I can find the exact definition of this statistics.

In my AWR report, it shows really high value for this stats:, what does it tell me, a physical IO problem or buffer contention in SGA?

Tablespace	Reads	Av Reads/s	Av Rd(ms)	Av Blks/Rd	Writes	Av Writes/s	Buffer Waits