Some content and links visible to your visitors on a web page may not actually be visible to the Search Engines, eg. Flash based content etc.. Part of your SEO research should include tools that will allow you to check that spiders see what they are supposed to see. I recently came across a tool which simulates a Search Engine by displaying the contents of a webpage exactly how a Search Engine spider would see it. It also displays the hyperlinks that will be followed (crawled) by a Search Engine when it visits the particular web page along with meta tags and description.
These are expressions that relate to links between websites, whether they are linking to your site from an external site, or relating to a link within your site going to a third party. For instance, you may want to link to a client, or a supplier may want to link to you.
The ‘follow’ status is used by indexing ‘bots’ (Google mini-programs that ‘spider’ the internet looking for links between sites) as an indication of whether any ‘kudos’ form the link should be shared from the source to the target. For instance a ‘do-follow’ link from a renowned site can be beneficial in terms of the way your site is viewed by a search engine. In most cases, links are ‘no-follow’ because Google regards the overuse of ‘do-follow’ links as generally a negative indication possibly flagging up a ‘link-farm’ trying to ‘game’ the indexing process.