Select Elements at Even Indexes $(":even")

$(":even")

e.g. $("li:even")

$(":even") selects elements at even indexes, e.g. 0,2,4,...etc within the matched set.

For example, $("li:even") will find <li> at even indexes within the matched set.
<ul>
<li>0</li>
<li>1</li>
<li>2</li>
</ul>
Example 2: $("div:even") will find <div> at even indexes within the matched set.
<div id='someID'>div-1</div> // index =0
<p>p-1</p>
<div class='someClass'>div-2</div>// index =1
<p>p-2</p>
<div>div-3</div> // index =2
<span>span-1</span>
Matched set is a set of elements matching selector. For example, in Example 2 matchted set is set of elements matching $("div") selector
<div id='someID'>div-1</div> //index = 0
<p>p-1</p>
<div class='someClass'>div-2</div> //index = 1
<p>p-2</p>
<div>div-3</div> //index = 2
<span>span-1</span>
jQuery selector filter $(":even")