What is NDJSON?

One JSON object per line, with no wrapping array. That small change is the whole point: a program can read a record at a time instead of parsing gigabytes into memory first, which is why log pipelines, bulk importers and search indexes all speak it.

What is SQL?

Not a file format so much as a language, but a file of INSERT statements is how data has always been moved into a database. Every engine will run one, and it's the least surprising thing to hand to a database that already exists.