also: クリスマスイヴ · クリスマス・イブ · クリスマス・イヴ
noun
Christmas Eve
Refers to the evening or entire day of December 24th, often associated with romantic dates and family gatherings in Japan.
クリスマスイブに彼氏とディナーに行く。
I'm going to dinner with my boyfriend on Christmas Eve.
子供たちはクリスマスイブにプレゼントを開ける。
The children open their presents on Christmas Eve.
Alternate spelling using ヴ; less common but still seen.
Spelling with interpunct; rarely used in practice.
Spelling with interpunct and ヴ; very rare.
クリスマス (Christmas) refers to the holiday itself, while クリスマスイブ specifically means the day before Christmas.
Borrowed from English 'Christmas Eve'.