It is a difficult question to answer as the names keep changing. And, in fact, there had never been a precise definition of a junior doctor.
Also, the term junior doctor is now obsolete, and been replaced by the term ‘resident doctor’. And, confusingly, this phrase also encompasses middle grade/experienced doctors called registrars (and specialty doctors).
Here is a timeline about training as a (typical) NHS hospital doctor, and current (and previous) titles and names.
Year 1. Medical Student (Age 18 years) – training starts
Year 2. Medical Student
Year 3. Medical Student
Year 4. Medical Student
Year 5. Medical Student, qualifying as a doctor
Junior doctor
Year 6. Foundation Year 1 (F1). Previous term = ‘House officer’, HO (or Junior House Officer, ‘JHO’)
Year 7. Foundation Year 2 (F2)
Year 8. Core or Specialty Trainee (CT1/ST1). If medical (not surgical), also called an ‘IMT’. Previous term = ‘SHO’ (Senior House Officer)
Year 9. Core or Specialty Trainee (CT2/ST2) – SHO
Registrar
Year 10. Core or Specialty Trainee (CT3/ST3) – Registrar. Previous term ‘SpR’ (Specialist Registar) and before that ‘SR’ (Senior Registrar)
Year 11. Specialty Trainee (ST4) – Registrar
Year 12. Specialty Trainee (ST5) – Registrar
Year 13. Specialty Trainee (ST6) – Registrar
Year 14. Specialty Trainee (ST7) – Registrar
Year 15. Specialty Trainee (ST8) – Registrar
Year 16. Consultant (Age 34 years) – training complete.
Note. Both junior doctors and registrars (and specialty doctors) are now different types of resident doctor.
For different types of doctor, the training is slightly different. For example, a GP does a 3 year GP training scheme after F1-2 posts and then can work independently.
We have described what the different types of junior (resident) doctors are called. Yes, it is confusing. But we hope it is a little clearer now.