Multi-Dimensional Arrays

Rectangular Arrays - These are really 2 dimensional. The number of rows is identical to the number of columns.
Jagged Arrays - These are not really 2 dimensional and represent a 1 dimensional array of 1 dimensional arrays. Each element in the main array can hold an array of varying length.

Arrays with mutiple dimensions are also referred to as jagged arrays.

string[,] asMulti = new string[5,5]; 

Conceptually, a multidimensional array with two dimensions resembles a grid. A multidimensional array with three dimensions resembles a cube.

int[,] array2D = new int[2,3]; 
int[,] array2D2 = { {1, 2, 3}, {4, 5, 6} }; 

for (int i=0; i<2; i++) 
{ 
    for (int j=0; j<3; j++) 
    { 
        array2D[i,j] = (i + 1) * (j + 1); 
    } 
} 

for (int i=0; i<2; i++) 
{ 
    for (int j=0; j<3; j++) 
    { 
        System.Console.Write(array2D[i,j]); 
    } 
    System.Console.WriteLine(); 
} 

int[] numbers = { 4, 5, 6, 1, 2, 3, -2, -1, 0 }; 
foreach (int i in numbers) 
{ 
    System.Console.Write("{0} ", i); 
}