JQuery Or $ Is Not Defined
It is a common issue in Jquery.
This is because the Jquery file (jquery.min.js) is not available.
jquery.min.js can be not available due to the following reasons.
1. If you havn't added the jquery.min.js file to your page.
3. If the jquery.min.js file is modified so that $ is not availalbe.
First of all add the Jquery file (jquery.min.js) to your page.
Adding Jquery file (jquery.min.js) on the Head Section is mostly preferred.
Always place your script file beneath the Jquery min file.
This will definitely resolve your issue.