<b>: The Bring Attention To element
developer.mozilla.org
developer.mozilla.org
Do not confuse the <b> element with the <strong>, <em>, or <mark> elements. The <strong> element represents text of certain importance, <em> puts some emphasis on the text and the <mark> element represents text of certain relevance. The <b> element doesn't convey such special semantic information; use it only when no others fit.
<b> was, is, and always will be the bold text element. No one is going to die if there is some slight semantic meaning in your HTML.
<b> and <i> for font manipulation (bold and italics)
<strong> and <em> for giving text importance (important and emphasized)
but honestly, I don't think it matters as long as you're consistent.