Emphasis
When a search engine spiders a web page, it scans the page looking for a number of different elements it considers important. Various factors are identified and incorporated into the overall calculation that decides a pages fate in the rankings. Among these many factors, is emphasis.
When developers emphasise text, for one reason or another, it is almost always keyword or keyphrase related. Search engines look for the right keywords that match you pages content, and it is the developers job to give these spiders a helping hand to inidicate what these keywords might be.
Emphasis is reference to text which in some way stands out from normal text, and because we can emphasise text in different ways, SEO weight is dependent on what form of emphasis is used.
Bold & Italics
Don't under estimate the power of bold, strong or italic emphasis. While web standards encourage the use of CSS font-weight attributes to embolden or italicise text, remember that their SEO weight is near invisible to spiders indexing page content.
Instead use
<strong></strong>,
<b></b>, or
<em></em> tags. Our aim is to make the search engines' job of find keywords as easy as possible, and using bold or italic emphasis here and there gives them a push in the right direction.
Header Tags
Give your web page a document outline. These weight quite heavily in comparison with the bold or italic emphasis used. Use them logically and legitimately, using the heirarchy provided.
Anchor Text and Links
Arguably the most powerful emphasis technique, and heavy weight contender in the whole business of SEO. Links are what glue the Internet together. Without links, you would have to type the URL into the address bar each time you viewed a different page.
Choose your anchor text wisely, and be careful not to send the search engine spiders down the wrong path. Many developers exchange reciprocal links with high ranking websites just to increase their own PR, but are penalised because the linked sites are not relational or relevant to the nature of the content on their own site.
Word of Warning
As always, don't over do it. Too much emphasis will drown your page and you will dilute or lose the desired effect. Remember, only placed emphasis around keywords that are relevant. Incorporate a heading/sub heading structure perhaps, allowing both header tags and bold emphasis in legitimate places.