What are inteins?

If the question is 'what are 'interns': In the US and many other countries, most medical doctors complete a post-medical school residency. This lasts usually 3-5 years and is a supervised period of medical practice that allows for eventual independent practice. During the first year of residency in most fields, the residents are called 'interns'. The are fully qualified to practice medicine, but are 'earlier' in training.