Inline elements are HTML elements that do not start on a new line and only take up as much width as necessary. They allow text and other inline elements to flow together seamlessly within a block of text. Common examples of inline elements include span, a (anchor), and img (image). Unlike block elements, which create a new line before and after themselves, inline elements can be placed next to each other. This makes them useful for styling specific parts of text or adding links without disrupting the overall layout of the page.