First: What is meant by a fellowship (Fellowship)?
A fellowship is an advanced, specialized training programme of short to medium duration (6 months to 3 years) that focuses on a very specific sub-field within your specialty (for example: microsurgical neurosurgery, interventional cardiology, paediatric oncology, etc.).
It is not considered an academic degree, but it is highly regarded professionally and enhances your job prospects, salary, and research career path.