Link building
An outbound-link (OBL) is a link from your website to another website. Outbound links can add value to your site by providing useful information to users without you having to create the content. It is difficult for a single website to be comprehensive about a subject area. At the same time outbound links are a potential jumping off point for users and also provide PageRank for the target page. Some search engines algorithms actually place value on sites with many outbound links. These are dubbed authority or expert sites.
Be careful about linking to bad neighbourhoods. These include LinkFarms and heavily optimized sites. These may get your site penalized. Be wary about any site with zero page rank or that can't be found in search engines. Check that it has not been banned for some reason. A single link to a bad neighbourhood is unlikely to cause problems but combined with other factors it could be viewed in a bad light by search engines.