lookup has two dimensions, this is how you can read them
double[,] lookup = { {1,2,3}, {4,5,6} };
int rows = lookup.GetLength(0); // 2
int cols = lookup.GetLength(1); // 3
int cells = lookup.Length; // 6 = 2*3
The concept of rows and cols is just tradition, you might just as well call the first dimension the columns.
Also see this question
