What does "App Concurrency" mean in the Grafana dashboard?

[Yaeger]

I figured it out, found it somewhere in a comment on a forum post:

Feature preview: Custom metrics

proxy_id - is to make sure the counters reset when we deploy or else it leads to some weird metrics. It’s possible we can have 2 proxies running concurrently while we gracefully shut down connections during a deploy. fly_app_concurrency - this is the current number of connections (or requests, depending on your concurrency config) established to your app instance