In my course, one defines $B_{n, d}(x)$ as “a basis of monomials of degree at most $d$.”
I also have an example for $n=1$ :
$$ B_{1, 2}(x) = \begin{pmatrix} 1\\ x\\ x^2 \end{pmatrix} $$
But I cannot find an example online of such a basis of monomials for more than 1 variable. For instance, what would $B_{2, 2}(x)$ be ? My guess would be something like
$$ B_{2, 2}(x) = \begin{pmatrix} 1 & 1\\ x_1 & x_2^2\\ x_1^2 & x_2^2 \end{pmatrix} $$
But I am really not sure.