What are jagged array?

The dictionary meaning of array is an orderly arrangement or sequential arrangement of elements.
In computer science term:
An array is a data structure that contains a number of variables, which are accessed through computed indices. The variables contained in an array, also called the elements of the array, are all of the same type, and this type is called the element type of the array.

Jagged array declaration in C#:
For e.g.: int [] [] myJaggedArray = new int [3] [];
Declaration of inner arrays:
myJaggedArray[0] = new int[5] ; // First inner array will be of length 5.
myJaggedArray[1] = new int[4] ; // Second inner array will be of length 4.
myJaggedArray[2] = new int[3] ; // Third inner array will be of length 3.
Now to access third element of second row we write:
int value = myJaggedArray[1][2];
Note that while declaring the array the second dimension is not supplied because this you will declare later on in the code.
Jagged array are created out of single dimensional arrays so be careful while using them. Don�t confuse it with multi-dimensional arrays because unlike them jagged arrays are not rectangular arrays.