There are two tags available that allow you to add emphasis to parts of your page content. To add some emphasis to a word or phrase you can surround it within <em> tags. To make the emphasis even stronger you can use <strong> tags.
<p> This sentence contains some words that need to be <em>emphasised</em> and some that require <strong>strong emphasis</strong>.</p>
Note that the purpose of these tags are to add emphasis to what they contain. When we use these tags we are not concerned with how the browser will indicate that emphasis particularly since web readers will apply the emphasis in how they speak the content of the tags while web browsers will change the styling of the text to indicate the emphasis. These are inline tags and so they must be contained within a block of text such as a paragraph or blockquote in order for their usage to be valid.
Most web browsers apply emphasis by displaying what is contained within <em> tags in italics and what is contained within <strong> tags in bold however browsers are not required to do this and using these tags to indicate text to be displayed in italics or bold is to use the tags the wrong way. As always when writing your XHTML the purpose of the tags is to indicate the type of content that you are entering - in this instance something that needs to be emphasised - and has nothing whatever to do with how that content is to be presented.
This article written by Stephen Chapman, Felgall Pty Ltd.