noun
A card that proves membership in an organization, club, or service.
会員券を見せてください。
Please show your membership card.
この会員券で割引が受けられます。
You can get a discount with this membership card.
会員証 is a more common word for 'membership card'. 会員券 is less frequent and may emphasize a ticket-like function (e.g., admission).
Compound of 会員 (member) + 券 (ticket/card).