It's tricky to define exactly, but I like this article's take on it: http://webdesign.about.com/od/tables/a/aa122605.htm

A list of emails can be thought of as tabular data. In Gmail, you have columns (selection, star, important, participants, subject, and date) with one row per email. That's a table without explicit headers.

Yeah, with current css specs in browsers you need to resort to table-cell stylings like display:table-row and display:table-cell. But that can be done without using actual <table> elements.