What is "5th Down R" ?

There's a dozen or so listings on eBay (exact same watch, different sellers) for Speedmasters from Japan with "5th down r" in the headline or description. But what is that? I've seen descriptions of the elongated r, so that must be part of it, but 5th? WTF they talking about?

The post by @machamp6650 is correct.
I'm Japanese, so I'll add a few things.
The 5th is ST145.022 in Japan.
The long R dial of the earlier ST145.022 is called "DownR" in Japan.
The term "5th DownR" is a direct translation of the Japanese term "5th 下がりR".
The ebay seller does not know the expression "Long R dial", so he translates it directly.

Simply put, in Japan, "5th down R" refers to the old ST145.022.

By the way, in Japan
1st CK2915
2nd CK2998
3rd ST105.003
4th ST105.012 and ST145.012
5th ST145.022
No specific ref is assigned from 6th ...
ST105.002 is also not specifically assigned...

Also, step dials are "段付き文字盤" in Japanese. I think can understand what it means by the literal translation here.

Great info, thanks everyone. I was afraid it was a Dumb Question (tm) that I hadn't thoroughly googled.