A list of lists is a way of creating a two-dimensional data structure in Python. In this case, each element of the main list is itself another list.

Here is a simple example of a list of lists in Python:

Here, list_of_lists is a list that contains three other lists. You can access elements in the list of lists by using two indices, where the first index is the position of the sub-list and the second index is the position of the element within that sub-list.

For example, if you want to access the number 5 from the list of lists defined above, you would do the following:

This would output:

This is because 5 is in the second sub-list ([4, 5, 6], where sub-list indexing starts from 0), and it’s the second element in that sub-list (again, with indexing starting from 0).

You can also modify elements in a similar way:

This would output:

In this case, we replaced the number 5 with 10 in our list of lists.