<strong> gives its content strong importance, seriousness, or urgency. Its usual bold appearance is a browser default, not its meaning.
Smallest working example
HTML and CSS
HTML
<p>
<strong>Do not share your password.</strong> Support will never ask for it.
</p>CSS
Edit HTML or CSS to update the preview as you type. Copy code snippet copies the selected tab. Preview spacing and font defaults are not included.
Use it in a sentence
Use it for an important warning within a paragraph. Nested strong elements indicate a greater degree of importance.
Placement and accessibility
This is phrasing content, so it fits inside a paragraph or another phrasing-content container. It accepts global attributes and has no required element-specific attributes. Keep the phrase understandable without depending on a visual font change. Screen readers and user settings vary; do not assume every reader will hear a different voice.
Choose the right alternative
Use b to draw attention without implying importance, em for stress emphasis, and font-weight for a purely visual change.
Sources and browser support
MDN: strong describes the syntax and links to the specification and compatibility data. Check individual values in that table when supporting older browsers.