"Underlined text" refers to words or lines of text that have a horizontal line drawn beneath them. It is often used to highlight or emphasize certain words or indicate a hyperlink on a webpage. Full definition
Although you can't use bullets, bold, or underlined text in a plain text document, you can use plus signs (+) at the beginning of lines to draw attention to part of your document. (dummies.com)
A word, or series of words, usually in blue underlined text, which when clicked with the mouse takes the user to another web page or to a different location in the current page. (gutenberg.net.au)
Using bold, italic and underlined text for emphasis is also noticed by search engines, so they should be used. (feedspot.com)