Big Data Definition

noun

Data sets that are too large to be processed easily by standard software.

Webster's New World

A collection of data sets so large and complex that it becomes difficult to process using on-hand database management tools or traditional data processing applications.

Wiktionary

Origin of Big Data

In 2000, economist Francis X. Diebold published the first version of a paper titled “Big Data Dynamic Factor Models for Macroeconomic Measurement and Forecasting." After being interviewed on his use of the term "big data" by NYTimes.com blogger Steve Lohr, Dieblold undertook his own investigation, in which he concluded: “The term Big Data, which spans computer science and statistics/econometrics, probably originated in the lunch-table conversations at Silicon Graphics in the mid-1990s, in which John Mashey figured prominently."

From Wiktionary
The Wikipedia article cites several sources from 2009 having "big data" in the title, which is when the term seems to have caught on. The same two words can be attested in the 1980s and 1990s, but not in the current sense of the term.

From Wiktionary