Refers to a job or workplace, often with a nuance of a position one has found or secured. Slightly formal.
He is looking for a new position.
It's great that you found a good place of employment.
Compound of 勤め (tsutome, 'work, service') and 口 (kuchi, 'opening, position'). The exact historical derivation is uncertain, but the combination naturally yields the meaning 'job opening' or 'place of employment'.