Document database
A database that stores each record as one flexible document, close to the shape the application code already uses.
What it tells you about a developer
Document database experience often points to fast-moving product work, because these databases favor shipping quickly over strict rules about data shape. A developer who has used both a document database and a relational one, and can say when they would pick each, has faced real data-modeling tradeoffs and is showing more depth than either name alone.
A document database stores records as self-contained documents, so two records in the same collection can have different fields. Teams pick one when data shapes change often or arrive messy. MongoDB is the best-known example, with Firebase and DynamoDB nearby. The umbrella term NoSQL covers document databases and several other non-relational kinds.