Perhaps the first challenge of big data is defining it adequately. It's a term so widely used as to be almost meaningless. For example, some may refer to data exceeding 1,048,576 rows as big data (that is, the row limit in Excel 2010 and 2013), while others would only apply the term to datasets in the multiple petabyte range. Definitions found on Wikipedia and Webopedia are so broad as to encompass both of these examples.
Note
Big data is a broad term for data sets so large or complex that traditional data processing applications are inadequate: https://en.wikipedia.org/wiki/Big_data
Big data is a buzzword, or catch-phrase, meaning a massive volume of both structured and unstructured data that is so large it is difficult to process using traditional database and software techniques: http://www.webopedia.com/TERM/B/big_data.html
True, we should probably not consider data that merely exceeds Excel's row limitation as big data; nevertheless, from the perspective of the...