The common way of preventing the default action of an event is to call preventDefault on its Event Object:

<a href="http://google.com">Google</a>
<script>
    // Prevent the default action (navigating to google.com)
    $( "a" ).on( "click", function( event ) {
        event.preventDefault();
    });
</script>

…which works just fine. But if all you need to do is prevent the default action, jQuery.fn.on provides a handy shorthand. Per its docs:

“The value false is also allowed as a shorthand for a function that simply does return false.”

Therefore, the same example could be written as follows:

<a href="http://google.com">Google</a>
<script>
    $( "a" ).on( "click", false );
</script>

The same approach will also work using delegated events:

<nav>
    <a href="http://google.com">Google</a>
    <a href="http://twitter.com">Twitter</a>
    <a href="http://facebook.com">Facebook</a>
</nav>
<script>
    $( "nav" ).on( "click", "a", false );
</script>

As noted in the comments, using the false shorthand is the equivalent of event.preventDefault(); event.stopPropagation();. Therefore when using the shorthand, the event will not bubble to parent elements (which may or may not be what you want to happen). The following example illustrates this:

<div id="container-1">
    <a id="a-1" href="http://google.com">Google</a>
</div>
<div id="container-2">
    <a id="a-2" href="http://google.com">Google</a>
</div>
<script>
    $( "#a-1" ).on( "click", function( event ) {
        event.preventDefault();
    });
    // When a#a-1 is clicked this will fire because the event's
    // propagation is not stopped.
    $( "#container-1" ).on( "click", function(){} );
    
    $( "#a-2" ).on( "click", false );
    // When a#a-2 is clicked this will not fire because the shorthand
    // stops propagation.
    $( "#container-2" ).on( "click", function(){} );
</script>