When using the DATEUNIT function to determine the year of a date, by default the result is displayed as an Integer number with thousand separators. Using Data > Manage Fields, we can reformat to remove the separators if we needed a plain integer displayed.
However, when using DATEUNIT as part of a larger function, to create a string YEAR + "Quarter 2" for example, the thousand separator cannot be so removed and the result, '2,009 Quarter 2' is far less preferable than '2009 Quarter 2'.
EEE is the shortened 3 character day format (EEEE would display full day name e.g. "Monday"). You can find the full list of date formats on this page: http://www.visokio.com/dates-and-times