Which HTML tag is used to define bold text?

The tag used to define bold text is the <b> tag. This tag is an inline element that visually renders text in a bold style. Historically, the <b> tag has been used primarily for stylistic purposes, simply indicating that the text should be presented in a bold font, without conveying any additional semantic meaning.

Though the <strong> tag can also render text in bold, its primary purpose is to indicate that the text has strong importance or emphasis, which provides semantic value and is beneficial for accessibility and search engines. The <em> tag is used to denote emphasis and usually renders text in italics, while the <bold> tag does not exist in HTML. Therefore, for the specific purpose of defining bold text in a straightforward manner without semantic implications, the <b> tag is the appropriate choice.