What is the difference between an all-India service and a service or post under the Union or a State?
The difference between an all-India service and a service or post under the Union or a State lies in their scope and jurisdiction. An all-India service is one that operates across the entire country, with officers serving various states as required by the central government. These services are managed by the central government, with recruitment and other administrative decisions taken at the national level.

On the other hand, a service or post under the Union refers to those in which an officer serves within the administration of the central government itself, while a service or post under a State refers to those where an officer serves within the administration of a specific state government. These services are managed by their respective governments (central or state), with recruitment and other administrative decisions taken at the relevant level.