Strange product of groups

Question

I am working on S. Mukai "Invariants and Moduli" (http://www.math.ens.fr/~benoist/refs/Mukai.pdf ) and on page 71 he writes in a Theorem:
\begin{align} "\text{.... then the ring of invariants under the action of } G \cdot T \cong \mathbb{C}^6\cdot (\mathbb{C}^{\times})^8 \subset GL(18, \mathbb{C}) \text{...} ". \end{align} I don't know what kind of product is meant here and have not found anything similar to this. So maybe someone has an idea. It seems a bit weird, that the product is a subset of the invertible $18 \times 18$-matrices... $\mathbb{C}^6$ is the additive group and $(\mathbb{C}^{\times})^8$ is the multiplicative group. $G \subset \mathbb{C}^N$ is a subspace of dimension $N-3$ and $T \subset (\mathbb{C}^{\times})^N$ is a subgroup of dimension N-1, if you need know this.