Are you really asking about "A" in AJAX . It means asynchrony and allows you to make a request without blocking . The callback function will be executed if / when the request is successful, but the rest of your code continues. One of the main advantages of this approach is the responsiveness of the user interface. A synchronous call will significantly freeze the browser until your request returns, which may take some time.
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$("input").focus(function () {
$(this).next("span").css('display','inline').fadeOut(1000);
});
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