ACID
Also written as Atomicity, Consistency, Isolation, Durability
A set of guarantees traditional relational databases make about transactions — that they complete fully or not at all, leave data in a valid state, don't interfere with each other, and survive a crash once committed.
Think of it like
Like a bank transfer that either fully completes (money leaves one account and arrives in the other) or doesn't happen at all — never half-finished, even if the power goes out mid-transfer.
Junior or senior?
Junior sounds like
Can recite the ACID acronym without explaining what it protects against.
Senior sounds like
Can explain what actually broke — or had to change in how they wrote code — when a system gave up strict ACID guarantees for scale.
Ask them
“What's a system you worked on that gave up strict ACID guarantees for scale? What had to change about how you wrote code against it?”