There are different "size" data sets.  The "size" is determined both by the computer storage required for its storage/transmission as well as the information/considerations that it entails.  Rough guidelines for data set size categories:

Tiny - Only alpha numeric information.  May be held in a rectangular excel spreadsheet with less than a hundred entries.  Considerations take at most two sentences to describe.

Small - Only alpha numeric information.  May be held in a rectangular excel spreadsheet with less than a thousand entries.  Considerations take at most four sentences to describe.

Medium - Only alpha numeric information.  May be held in a rectangular excel spreadsheet with less than ten thousand entries.  Considerations take at most eight sentences to describe.

Large - Only electronic information.  Less than 100 megabytes of storage required.    Considerations take at most one page to describe in words.

Huge - Only electronic information.  Less than 10 gigabytes of storage required.    Considerations take at most ten pages to describe in words.

Big Data - The sky is the limit!