Span <span> is a generic inline element. It does nothing, visibly, by default and has no semantic meaning, unlike the vast majority of the other inline elements. It is typically used to allow regions of text or other inline elements to become full elements with classes/ids/local styles for styling and scripting reasons. Text blocks, e.g. all the text inside a paragraph, is treated as one monolithic text node if there aren't any inline elements in it.
Examples:
<!--Give it a class-->
<!--maybe class soAngry is blinking, red, big and bold
.soAngry{
text-decoration:blink;
color:red;
font-size:xx-large;
font-weight:900;
}
-->
You did <span class="soAngry">WHAT?!?!</span>?
<!--Give it an id for JavaScript-->
Is your name <span id="mutable">Bob</span>?
<button onclick="document.getElementById('mutable').setAttribute('class','soAngry');">Hate Bob</button>
<button onclick="document.getElementById('mutable').setAttribute('class','');">Like Bob</button>