One of the common uses for the 名詞（めいし） (noun) 後（あと） ‘behind’ is to express a remainder, or everything after a certain point. This can be translated as ‘what’s left of (A)’, ‘the rest of (A)’, ‘what’s remaining of (A)’, or even ‘other than (A)’. Let’s have a look at a few examples.
後（あと） will be grouped with the 格助詞（かくじょし） (case-marking particle) の before nouns, come directly before numbers, or be used at the beginning of whole phrases.
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今（いま）あなたが持（も）っている段（だん）ボール箱（ばこ）はキッチンまで運（はこ）んでおいてください。後（あと）の段（だん）ボール箱（ばこ）は全部（ぜんぶ）寝室（しんしつ）までお願（ねが）いします。
Please bring the cardboard box you are carrying into the kitchen. Please take all the rest to the master bedroom.
後（あと）ちょっとで着（つ）くからもうちょっと我慢（がまん）して。
We will arrive in a little bit, so please be patient for a little longer.
映画（えいが）公開（こうかい）まで後（あと）3日（か）！
Three days left until the movie gets released!
Despite having many different translations, the base meaning of 後（あと） will always just be to identify a sequence of things, and what comes ‘after’ or ‘behind’ a specific point in that sequence.