It's becoming common. You can also hear "jagged tensors". Alternatively "ragged".

I've heard the term before, but I have never needed to use jagged arrays.

It is, although at both schools I went to "ragged arrays" was the more common term.

https://en.wikipedia.org/wiki/Jagged_array

I think to some degree it's fallen out of favor as this is the only kind of array you will ever see if you stick to, say, bootcamp-level Python and JavaScript.

It's common parlance in C# where the language has different syntax for dense and jagged arrays (i.e., A[i,j,k] vs A[i][j][k]).