What is the difference between JavaScript and jQuery?

JavaScript is a language whereas jQuery is a library written using JavaScript.

JQuery is a fast, lightweight JavaScript library that is CSS3 compliant and supports many browsers. The jQuery framework is extensible and very nicely handles DOM

manipulations, CSS, AJAX, Events and Animations.
Mask:

$(document).ready(function() {
    // Attaches masks to page controls
    $('#<%= txtSsn.ClientID %>').mask("999-99-9999");
    $('#<%= txtBirthDate.ClientID %>').mask("99-99-9999");
});