noun
available day (for a venue or facility)
Refers to a day when a place (e.g., a meeting room, event hall, sports facility) is free and can be used.
会議室の空き日を確認してください。
Please check the available days for the meeting room.
noun
free day (for a person)
Refers to a day when a person has no plans and is available.
来週の空き日を教えてください。
Please tell me your free days next week.