Once upon a time, “big data” was datasets large enough that it was impractical to try to store or work with them in a traditional relational database software. Which is where distributed structures came into play with the ability to spread both storage and computation across clusters of machines, using solutions like Hadoop and MongoDB. That seemed to be the direction things were heading 10 - 15 years ago.

However, with the automated scaling built into modern cloud databases, the line has gotten a bit blurry; Snowflake, Redshift, BigQuery all handle many billions of rows just fine. I probably wouldn’t use the term big data in a professional context these days, but there is a table size after which I write code a bit more carefully.

I suppose my point is that the term once meant something, but marketing stole it because it sounds cool. I worked in a tech shop in the late aughts where the sales team insisted on calling every rack mounted server a “blade server”, regardless of whether it had modular swappable boards. Because it sounded cool.