The top of your Plugin’s main PHP file must contain a standard Plugin information header. This header lets WordPress recognize that your Plugin exists, add it to the Plugin management screen so it can be activated, load it, and run its functions; without the header, your Plugin will never be activated and will never run. Here is the header format:
<?php
/**
* Plugin Name: Name Of The Plugin
* Plugin URI: http://URI_Of_Page_Describing_Plugin_and_Updates
* Description: A brief description of the Plugin.
* Version: The Plugin's Version Number, e.g.: 1.0
* Author: Name Of The Plugin Author
* Author URI: http://URI_Of_The_Plugin_Author
Also note the name of plugin i.e.(plugin_name.php) and Plugin name in header should match and be unique.