Questions & Answers about Ferien er i august.
Because -en marks the noun as definite singular in Norwegian.
- ferie = a holiday / a vacation
- ferien = the holiday / the vacation
So ferien er i august refers to a specific holiday or vacation that is already known from the context.
Yes, ferien is grammatically singular.
That can feel a little strange to English speakers, because English sometimes uses plural expressions like the holidays or the summer holidays. Norwegian often uses a singular noun where English might use either singular or plural, depending on dialect and context.
So in this sentence, the grammar is singular even if the English translation might sometimes sound more natural in the plural.