From Diablo Wiki
HRs refers to Diablo 2's high level. This term may be reused for high level runes in Diablo III, but in common parlance it refers to high level runes in Diablo II; how high is high is open to debate, but the term generally refers to at least the rune (r24) and higher.
- More reference terms.
Unit of Currency
Since gold was basically worthless in Diablo II, players soon adopted other items as units of trade. Gems were traded at various times, but early on in the days of D2C, the Stone of Jordan became the default currency. Top quality items were priced in terms of how many SoJs they were worth, and this value led to massive duping of SoJs, which depressed prices and made it impossible for legitimate players to keep pace with the currency, since finding items was much slower than cheating/duping to create them.
The SoJ lost its place as the chief item of currency during later patches of D2X, as high level runes (HRs) took over that role in the economy. They were duped just as badly as the SoJ had ever been, given their value as currency, and more over their utility for creating runewords.
See the economy article for much more detail about how Diablo III's economy will function and which items may become units of currency in the game.