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.

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.