The class in html is an attribute which can be used on any element, multiple elements can share a class, and multiple classes can be applied to one element. The attribute is often used to accurately target an element or a group of elements from a CSS stylesheet or JavaScript code.
Multiple classes on an element are separated by a space: class="class1 class2" would apply both class class1 and class2 not one class class1 class2
Example
<h1 class="bold uppercase">Heading</h1>
<p class="uppercase">Paragraph</p>