How to call this "SortedDict 2D" data structure?

Recently I come across a need for a 2D data structure like this, but I am not sure how to call it. Any advice how to call it?
For example I have a data structure (called SortedDict2D) containing this table:

        1           3
-------------------------
"a" |  "a1"        "a3"
"c" |  "c1"        "c3"

It looks like a SortedDict 2D, for example if I insert horizontally
insert_h!( dict2D, “b” )
it will become

       "1"         "3"
-------------------------
"a" |  "a1"        "a3"
"b" |  "b1"        "b3"
"c" |  "c1"        "c3"

If I insert vertically:
insert_h!( dict2D, 2 )
it will become

       "1"     "2"     "3"
-----------------------------
"a" |  "a1"    "a2"    "a3"
"b" |  "b1"    "b2"    "b3"
"c" |  "c1"    "c2"    "c3"