The important part you need to know in that case isn't the definition of ACID, but the actual transactional properties of the database you're working with. And

The important part you need to know in that case isn't the definition of ACID, but the actual transactional properties of the database you're working with. And even among developers working with databases, it varies how well you actually need to understand transactions. And I would guess that many developers working with relational databases don't actually understand the more subtle differences between transaction isolation levels. I think asking backend developers to know the basics of transactions is reasonable. But e.g. knowing the exact difference between READ COMMITTED, REPEATABLE READ and SERIALIZABLE (and what your specific database actually implements there) might not be necessary in many cases. Though it certainly is good to be able to spot when you're about to enter territory where these differences might matter. I agree that a backend developer working with databases should know what transaction are. But I don't really need the definition of ACID, and you can really push this question into details that are not relevant for all developers.