HTML5

The HTML <span> element is a generic inline container for phrasing content, which does not inherently represent anything. It can be used to group elements for styling purposes (using the class or id attributes), or because they share attribute values, such as lang. It should be used only when no other semantic element is appropriate. <span> is very much like a <div> element, but <div> is a block-level element whereas a <span> is an inline element.

font-weight: bold

The HTML Strong Importance Element (<strong>) indicates that its contents have strong importance, seriousness, or urgency. Browsers typically render the contents in bold type.

The <em> element is for words that have a stressed emphasis compared to surrounding text, which is often limited to a word or words of a sentence and affects the meaning of the sentence itself.

Typically this element is displayed in italic type. However, it should not be used simply to apply italic styling.

font-style: italic.

The HTML Abbreviation element (<abbr>) represents an abbreviation or acronym; the optional title attribute can provide an expansion or description for the abbreviation. If present, title must contain this full description and nothing else.

The HTML Mark Text element (<mark>) represents text which is marked or highlighted for reference or notation purposes, due to the marked passage's relevance or importance in the enclosing context.

Use this more or less only for to mark the most relevant search result!

The meter element can be used to mark up measurements, provided that those measurements are part of a scale with minimum and maximum values.

meter is not for progress bars, use progress instead!