.h is a header file which includes standard input and output
functions

u know that every file is exist with extention name
so .h is a extention name of all header file.

thanks both of u ...4r giving d answer

this is called as a header file..... like .txt in
editors.... in this this header file dosent belong to the C
code..... the meaning of this is in this .h files all
functions will be writtern .............. eg. string
fun(),I/O fun(),getch(),clrscr(),math functions() ...... etc
... etc

it is a header file.it stands for"standard input and 
output"file.if you want to give any input to the computer 
or if you want to recieve any output from the computer
(printf,scanf)this header file must be used.

this header file include EOF function also

.h Means header file of input output in c.
#include<stdio.h>
it means standered input output header file.

accrding to my view simply we can say #include<stdio.h> is
a header file .this is include all standered input output of c
.h is used in this syntex is represents the link about the
header file (.h)
         we also write syntex #include<stdio.h> is
#include"stdio.h"    the .h shows that this is a header file..

.h is the extention of the header file
h indicates that its a header file