What is partial class in c#

A partial class splits the definition of a class over two or more source files. You can create a class definition in multiple files but it will be compiled as one class.

Refer this links..

1 ) Partial Classes in C# With Real Example

2 ) Partial Classes and Methods (C# Programming Guide)

3 ) C# Partial

Patial class is used to divide a class or view physically,not logically to maintain code.
suppose i have a class Customer , i can divide it to  two or more partial class such as
 public partial class customer1
{
} 
and
 public partial class customer2
{
}