Officer on Special Duty (India)
"...There are two principal critieria in appointing an OSD in the civil services -
- When an officer by his appoinment brign far greater economic benefit to the government than that spent in his appoinment
- When there is an obligation on the government to take a certain action for the benefit of the larger good..." 
It is also sometimes used as a training post for a future higher level posting. For example, when S.Ranganathan was appointed the Comptoller and Auditor General, he was first appointed as an OSD to understudy the outgoing CAG A.K.Roy and subsequently given charge.