mathematics - Is there a name for a "non-rectangular matrix"?

According to Wikipedia a matrix in the mathematical sense is a rectangular array of numbers.

So this:

  1 2 3 4  
  5 6 7 8 
  7 8 9 10

would be an example for a matrix, while the following would not be a matrix:

  1 2 3
  4  
  7 8

What would be a good term for the latter, which is also a 2-dimensional field of numbers like a matrix but not rectangular?

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Regarding the comment that I could just add zeros, actually that is not possible and would be a different thing, since this does come from a technical background where any element of one row can be chosen at random and increasing the length of one row has other side effects that aren't intended.
It's also not a partial matrix the elements in the shorter rows really are not there and are not free to be chosen.