"lel999" wrote:
What does { } mean in excel formulas?

They are called curly braces.

And there meaning depends on where you see them.

If you see them in a context like OR(A1={1,2,3}), the curly braces delimit
an array of constants.

If you see them in the Formula Bar in a context like
{=AVERAGE(IF(A1:A100<0,A1:A100))}, the curly braces denote an array-entered
formula. That is, a formula that was entered by press ctrl+shift+Enter
instead of just Enter.

Unlike array constants, we cannot type the curly braces around an
array-entered formula. Excel simply displays them to let us know the
formula was array-entered.

Note that I say "array-entered", not "array formula". The latter term is
ambiguous and debatable.

For example, some people call =SUMPRODUCT(A1:A100,B1:B100) an "array
formula". And some people reserve the term "array formula" to denote a
multi-cell array-entered formula like =LINEST(Y1:Y100,X1:X100), in contrast
to a single-cell array-entered formula like
=AVERAGE(IF(A1:A100<0,A1:A100)).

So, to be clear, I use the term "array-entered" if I am referring to a
formula that should entered by pressing ctrl+shift+Enter.