Stands for "fiscally conservative socially liberal." Precisely the group left out in the cold in the two-party system of the United States.
Susan: George told me he didn't even vote in 2008! How could he!
Megan: Well, he's a FCSL.
When one writes an email that is intended to have an attachment, but the author forgets to actually attach the document before it is sent.
Email 1:
Joe, here's that excel spreadsheet you requested. See attached.
Fred
Email 2:
Fred, you mean "see unattached"? You forgot the excel file.
Joe