In the US, an academic postdoc is a training position with a shamefully low salary and without provision for advancement, somewhat analogous to a medical intern

In the US, an academic postdoc is a training position with a shamefully low salary and without provision for advancement, somewhat analogous to a medical internship. It's a job, but not a career. Depending on location, there may be mechanisms to preferentially hire a postdoc on as non-tenured faculty. It became more common in biomedical sciences after the recession when grad students stayed on for "postdocs" with their advisors when they couldn't find a job, and were then aged out of the postdoc.