What is Define() function in Netsuite SuiteScript 2.0

In SuiteScript 2.0 , script uses define() function to load the modules before execution

Use the define() function to load SuiteScript 2.0 modules and create custom modules.
When you use the define() function, it loads all dependencies before it executes any logic.
In SuiteScript 2.0, the define() function returns an object that encapsulates the module you are defining.

Developer must use the define() function in his/her entry point script. The return statement must include at least one entry point and entry point function. All entry points must belong to the same script type. 

/**
 * @NApiVersion 2.x
 * @NScriptType UserEventScript
 */
define(['N/record'],
    function (record)
    {
        function method1(context)
        {
            //add your logic here
        }
        function method2(context)
        {
           // add your logic here 
        }
        function method3(context)
        {
            // add your logic here 
        }
        return {
            beforeLoad: method1,
            beforeSubmit: method2,
            afterSubmit: method3
        };
    });