ThisWorkbook doubt

Hello Seniors,
I have a line of code as follows

ThisWorkbook.Greencard = True

My question is, is "Greencard" a name of the sheet and if it is what does the above code do

The entire finction is as follows


Private Sub btnGreenCards_Click()
GreencardReport
ThisWorkbook.GreenCard = True
End Sub

In my excels spreadsheet there is no sheet named GreenCard there is one named Green Cards. I am in a fix please help me out.
Waiting for replies

Regards,
Amandeep