How to Add an Underline to Text in HTML

Underline is a text decoration that draws a line below the text. It is used to emphasize the importance or relevance of the text, or to distinguish it from other text on the page.

In HTML, you can use the `text-decoration` property to add an underline to text. For example:
```

This text has an underline.

```
You can also use the `underline` property specifically to add an underline:
```

This text has an underline.

```
The number after the `underline` property specifies the thickness of the underline. A higher number will make the underline thicker.

It's worth noting that some browsers may not support all text decoration properties, so you may need to use a fallback method (such as using a CSS gradient or background image) if you want to ensure that your text is displayed with an underline in all browsers.