Deputation means to go from one department to another department for specified period.
Advantages of deputation:
1) Seniority remains in the parent department
2) Pay will be given of the department to which one is deputed.
3) After specified period you can got to your parent department.

Example
From District police one is deputed to Motor way or FIA
seniority will be of District Police and pay will be given by Motor way Police.

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