this is a contextual or just parent element:
var icon = $('.icon', this);
Here, this refers to an element that contains an element with the icon class.
You can also write it like this:
var icon = $(this).find('.icon');
In fact, you pasted into partial code, here is an example:
$('#someID').mouseenter(function(){ $('.someClass', this).addClass('myClass'); });
In the above code, this refers to an element with id someID .
You can get more information here:
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