What is this letter?

Question

What is the highlighted letter and how do I pronounce it?
(When I copy and past it to a text editor, I came out as 'G')

I am currently studying an ICWSM 2018 paper: "DEBATENIGHT: The Role and Influence of Socialbots on Twitter During the First 2016 U.S. Presidential Debate"

An unknown character came out while I was reading section 3.1

Answer 1

It's an uppercase in a script or calligraphic font. It looks like the document was prepared with LaTeX, and in MathJax you can write $\mathcal{G}$ to get $\mathcal{G}$.

Your excerpt is:

temporal order as cascade $C \in \mathcal{G}$, we call each diffusion tree a diffusion scenario $G \in \mathcal{G}$. Fig. 1a contains a cascade...