How do you call it when you stack vectors on top of each other?

Question

How do you call it when you stack two vectors, let's say $u=\pmatrix{u_1\\u_2}$, $v=\pmatrix{v_1\\v_2}$, on top of each other such that you get $$u\oplus v=\pmatrix{u_1\\u_2\\v_1\\v_2}?$$ I found this notation in this paper, chapter II.A. From what I could find I suspect it is either a direct sum or a Kronecker sum but I don't know how those sums apply to vectors, only matrices.

Answer 1

Looking at Notation for set of concatenated vectors?, as @JMoravitz says, "concatenation" is probably the best name for it. Notationally, it's quite common to write this as $$w = \pmatrix{u\\v}$$ where $u \in U, v \in V, w\in W \cong U \oplus V $.

This is basically the same notation as block matrices, where the "matrix" in question is $n \times 1$.