What is the difference between HTML tags DIV and SPAN?

div is a block element, span is inline.

This means that to use them semantically, divs should be used to wrap sections of a document, while spans should be used to wrap small portions of text, images, etc.

For example:

<div>This a large main division, with <span>a small bit</span> of spanned text!</div>

Note that it is illegal to place a block level element within an inline element, so:

<div>Some <span>text that <div>I want</div> to mark</span> up</div>

...is illegal.

You asked for some concrete examples, so is one taken from my bowling website

<div id="header">
    <div id="userbar">
        Hi there, <span class="username">Hidayt Rahman</span> |
        <a href="/edit-profile.html">Profile</a> |
        <a href="http://hrwebguru.blogspot/_ah/logout?...">Sign out</a>
    </div>
    <h1><a href="/">Bowl<span class="sk">SK</span></a></h1>
</div>