Bold definition
Bold:
A way to make words appear in a bolder font. Words that appear in a bolder font are more likely to be read by humans that are scanning a page. A search engine may also place slightly greater weighting on these words than regular text, but if you write natural page copy and a word or phrase appears on a page many times it probably does not make sense or look natural if you bold ever occurrence.
Most glossary items from Aaron Wall's SEO Book.
