union station; joint station
A railway station used jointly by multiple railway companies. Common in contexts where different operators share the same station facilities.
This station is a joint station used by JR and a private railway.
共同使用 means 'joint use' or 'shared use' in general, while 共同使用駅 specifically refers to a station shared by multiple railway operators.
Compound of 共同 (joint, shared) + 使用 (use) + 駅 (station). A straightforward modern technical term.