Trusted Source: A trusted source is simply a link to a more trustworthy website. This type of link is more likely to count in search engine results than one that is from an obscure, rarely used, or rarely cited website. For more information, see the entry for "Quality Link."
A trusted source will often be linked by other, more trusted sites on the internet. However, sometimes good links can be cited by bad websites in an effort to boost their own authority. Additionally, a page with many links are often looked at as lower quality pages, as they may be taking part in a spamdexing effort.
Although it can be edited by just about anyone, Wikipedia is considered a trusted source by Google and often appears high in search engine results for various keyword queries. Wikipedia is often cited on the internet, and the site's administrators regularly check pages for quality content and citations, among other site requirements. Wikipedia is also generally free of duplicate content, malicious links, and other factors that would get the site banned from Google's results.
There is also a website called TrustedSource.org, run by McAfee, which scores the reputations of various internet identities, such as IP addresses, URLs, domains, and content for email or the web.