TITLE: What does $\textstyle y \in \Re^{100}$ mean?
QUESTION [8 upvotes]: Just reading online and came across this:
$\textstyle y \in \Re^{100}$
I am guessing it's something like "y is an element of [something about real numbers]".  Can anyone help me out?

REPLY [2 votes]: It is just "Fraktur", a German typeface, emphasizing of $R$, thus $\mathfrak{R}$, instead of the usual "blackboard bold" emphasizing $\mathbb{R}$ or plain bold $\bf{R}$
A frequent use of $R$ for a set is the set of real numbers.
And the given expression is likely to be the Cartesian product of the set $R$, thus $100$-tuples with components from $R$.