In the Kubernetes/Docker ecosystem there is a convention of using /healthz as a health-check endpoint for applications.
Where does the name 'healthz' come from, and are there any particular semantics associated with that name?
It historically comes from Google’s internal practices. They're called "z-pages".
The reason it ends with z is to reduce collisions with actual application endpoints with the same name (like /status). See this talk for more: https://vimeo.com/173610242
Similar endpoints (at least inside Google) are /varz, /statusz, /rpcz. Services developed at Google automatically get these endpoints to export their health and metrics and there are tools that collect the exposed metrics/statuses from all the deployed services.
Open source tools like Prometheus implement this pattern (since original authors of Prometheus are also ex-Googlers) by coming to a well-known endpoint to collect metrics from your application. Similarly OpenCensus allows you to expose z-pages from your app (ideally on a different port) to diagnose problems.