Alfredo,
It means that it is an array formula. The formula is being used to resolve
each cell in the array presented. So in your example, each cell in B4:B7 is
tested against C17, and if true, the corresponding value in G4:G7 is
returned, which gets summed by the SUM formula.
You don't enter {} yourself, Excel does it when you tell it (Excel) that you
want to use array formulae by typing the formula in and using
Ctrl-Shift-Enter rather than just Enter.
--
HTH
Bob Phillips
... looking out across Poole Harbour to the Purbecks
(remove nothere from the email address if mailing direct)