Correct word for work vacant, place, employment

Correct word for work vacant, place, employment

I am designing a software application where we deal with organizational
charts. We need to store the Area and Position (job title) of an employee.
We also store the functions and tasks of that employee in that position.
Because an employee may leave the organization and his/her tasks must
remain for the next employee in his/her position, we need to name this
area-position entity.
What I want is a word to describe this. Candidates I found are 'vacant',
'place', 'employment', 'job'.
Thanks!