What is NDJSON?
NDJSON is one JSON object per line, and nothing wrapping them. That single change makes it streamable - a program can handle a line at a time instead of holding the whole array in memory - which is why logs, data exports and machine-learning datasets ship in it.
What is XML?
XML is the verbose, strict ancestor of most structured data formats, and it is still what enterprise systems, publishing pipelines and older APIs exchange. Tabular data in XML is usually a repeating row element with one child per column.