Given a quadratic matrix $A=\begin{pmatrix} a_{11}& a_{12} &...& a_{1n}\\ a_{21} &a_{22} & ... & a_{2n} \\ \vdots & \vdots & \ddots & \vdots \\ a_{n1} & a_{n2} & ... & a_{nn}\end{pmatrix}$, the set $\{a_{i,j}: i-j=0\}$ is called the diagonal. What do you call the set $\{a_{i,j}: i-j=k\}$ for a fixed $k$?
In German, there is the name "Nebendiagonale" (see e.g. https://de.wikipedia.org/wiki/Nebendiagonale). I am also familiar with speaking of the "erste (first) Nebendiagonale", "zweite (second) Nebendiagonale" etc. for the first or second "diagonal" below/above the main diagonal, when it is clear that we are talking about upper/lower triangular matrices. Google was no help to me.
Could you tell me the Englisch term?
Thank you!