Nearly completely empty; virtually empty—used when places like trains or venues have very few people (read as がらあき).
日曜の昼間だから駅はがら空きだ。
It's Sunday afternoon, so the station is practically empty.
映画館の一番前の席ががら空きだったので、そこで観た。
The front row in the cinema was empty, so I watched from there.
平日の昼間はレストランががら空きで予約なしでも入れる。
On weekday afternoons the restaurant is almost empty and you can get in without a reservation.
Inadequately defended; unguarded or exposed—used for places or positions that are poorly defended or vulnerable.
敵の側面ががら空きだったので、そこで攻め込んだ。
The enemy's flank was wide open, so we attacked there.
セキュリティががら空きの建物は盗難のリスクが高い。
A building with poor security is at high risk for theft.