"Resigning" in service terminology? (9,4,4)

I believe the answer is:

deserting ones post

I'm a little stuck... Click here to teach me more about this clue!

'service terminology?' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'resigning in' is the wordplay.
I cannot quite understand how this works, but
'in' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.