Name for the top left cell of a table

Solution 1:

The top left corner of any display is called the Canton in English heraldry.
In the U.S. flag, for instance, the blue part with white stars is the canton.

In a table, it's usually blank because the top row and left column are labels, not data;
so whatever appears in the top left box can't be either. Thus it's available for special purposes.

Solution 2:

It’s called the northwest corner cell.

For example:

Select the northwest corner cell of the transportation table and allocate as many units as possible equal to the minimum between availability supply and demand. . . .

Solution 3:

It is called first header cell, especially in programming.

It is also mentioned in the table style element order on MSDN site.