what is meaning of <iostream>

Answer 1

this a library, it gives you access to most of the functions you use in every program

Answer 2

it is a header function..to be precise <iostream.h>- input output stream header file 
Provides functionality to use an abstraction called streams specially designed to perform input and output operations on sequences of character, like files or strings. 
Objects cin, cout are from iostream header. 

Answer 3

Input output stream. It is the function for cout and cin statements