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 HTML?

The web's document format, and incidentally a place an enormous amount of tabular data ends up - published tables that were never offered as a download. Pulling those out is usually easier than asking whoever published them for the numbers.