Heisenberg used this operation to create a matrix from multiple vectors.
$$x=\begin{pmatrix} \circ \\ \circ\\\circ\\\vdots \end{pmatrix}, y= \begin{pmatrix} \triangle\\ \triangle\\\triangle\\\vdots \end{pmatrix}, z= \begin{pmatrix} \square\\ \square\\\square\\\vdots \end{pmatrix}\ldots$$$$U = \begin{pmatrix} \circ & \triangle & \square & \ldots \\ \circ & \triangle & \square & \ldots \\ \circ & \triangle & \square & \ldots \\ \vdots&\vdots&\vdots \end{pmatrix}$$
What do you call this operation?
In most math softwares, this operation is known as concatenation.
In abstract algebra or computer programming among other fields, concatenation of strings corresponds to joining strings together without intermediate operator or delimiter. This notion naturally extends to arrays and matrices.