Using @ in excel formulas?

I looked online but can't find anything regarding using @ in formulas.

I was looking at an old spreadsheet from a previous worker and came across these formulas...can someone help with what they are especially the @ symbol?

=IF([@[Cost Model]]="CPM",[@[Unit Revenue]]*[@[Ordered Units]]*0.001,[@[Ordered Units]]*[@[Unit Revenue]])

=MAX(IF([@[Cost Model]]="CPM",[@[This Month''s Goal]]*[@[Unit Revenue]]*0.001,[@[This Month''s Goal]]*[@[Unit Revenue]]),0)


=IF([@[Cost Model]]="CPM",MIN([@[Month''s Units (Adv)]]*[@[Unit Revenue]]*0.001,[@[Revenue Cap]]),MIN([@[Month''s Units (Adv)]]*[@[Unit Revenue]],[@[Revenue Cap]]))

click the example.PNG that is not in the grey box, they are both the same except that the one in the grey box doesn't show the cells highlighted

Thanks for your help!