What is remote action in Salesforce?

Remote action function in salesforce allows the user to access any method from any class through javascript methods, and get the result as a javascript object for further manipulation.

While implementing remote action function remember:

Remote action method should have @RemoteAction annotation. The method should also be Global and Static
Implementation
Let’s start with the controller code:

global with sharing class ContactJs {  

    public ContactJs() { }  
    @RemoteAction
    global static list<Contact> getcon() {
        list<Contact> con1 = [SELECT id,name FROM contact limit 5];
        if(con1!=null && !con1.isEmpty()){        
            return con1;        
        }else{        
            return  new list<contact>();        
        }
    }
}

Now the Visualforce Page:

<apex:page controller="ContactJs">
    <script type = "text/javascript">
    function getRemoteContact() {
        var a;
        Visualforce.remoting.Manager.invokeAction(
            '{!$RemoteAction.ContactJs.getcon}',
            function(result, event){
               if(event.status){
                    document.getElementById('remoteContactId').innerHTML = 'Contact Name: <br/><br/>';
                    for(a=0;a<result.length;a++){                        
                        document.getElementById('remoteContactId').innerHTML +=  result[a].Name +'<br/>';                    
                    }                                       
               }               
            },
            {escape: true}
        );
    }
    </script>
    <button onclick="getRemoteContact()">Get Contact</button>
    <div id="responseErrors"></div>
    <apex:pageBlock id="block">        
        <apex:pageBlockSection id="blockSection" columns="2">
                <span id="remoteContactId"></span>
        </apex:pageBlockSection>
    </apex:pageBlock>
</apex:page>