In general, what is the algebaic group $\mathbb{G}_m$ ? However I am looking in the textbook it says: $$ \mathrm{Res}_{E/F}(\mathbb{G}_m) \,/\, \mathbb{G}_m $$ where $E$ is an extension of $F$ with $[E:F] = n$. And the book calls this a torus.
The answer might appear in this book of David Witte Morris which is 600 pages. I found many instances of the word "torus" but none with the blackboard $\mathbb{G}$.