Rails + New Relic: What does RPM mean?

I just started using New Relic RPM with my rails app, and one of the metrics they provide is "Throughput RPM". I have googled everywhere and thoroughly combed the New Relic docs, and I cannot find ANY written explanation of the RPM throughput metric.

Is it "requests per minute" or "requests per millisecond" or something else? ** combustion engines and revolutions per minute make this impossible to find answers about in Google.

What is throughput RPM? Is a good number higher or lower, what are some average benchmarks, etc?

I'd greatly appreciate an explanation of this metric, thanks!!