Jquery mouseenter() vs mouseover()

The mouseenter event differs from mouseover in the way it handles event bubbling. The mouseenter event, only triggers its handler when the mouse enters the element it is bound to, not a descendant. Refer: https://api.jquery.com/mouseenter/

The mouseleave event differs from mouseout in the way it handles event bubbling. The mouseleave event, only triggers its handler when the mouse leaves the element it is bound to, not a descendant. Refer: https://api.jquery.com/mouseleave/

You see the behavior when your target element contains child elements:

http://jsfiddle.net/ZCWvJ/7/

Each time your mouse enters or leaves a child element, mouseover is triggered, but not mouseenter.

$('#my_div').bind("mouseover mouseenter", function(e) {
  var el = $("#" + e.type);
  var n = +el.text();
  el.text(++n);
});

#my_div {
  padding: 0 20px 20px 0;
  background-color: #eee;
  margin-bottom: 10px;
  width: 90px;
  overflow: hidden;
}

#my_div>div {
  float: left;
  margin: 20px 0 0 20px;
  height: 25px;
  width: 25px;
  background-color: #aaa;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>

<div>MouseEnter: <span id="mouseenter">0</span></div>
<div>MouseOver: <span id="mouseover">0</span></div>

<div id="my_div">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

Though they operate the same way, however, the mouseenter event only triggers when the mouse pointer enters the selected element. The mouseover event is triggered if a mouse pointer enters any child elements as well.

See the example code and demo at the bottom of the jquery documentation page:

http://api.jquery.com/mouseenter/

... mouseover fires when the pointer moves into the child element as well, while mouseenter fires only when the pointer moves into the bound element.