Link juice is the term used in the SEO world to refer to the value or equity passed from one page or site to another. This value is passed through hyperlinks. Search engines see links as votes by other websites that your page is valuable and worth promoting.
Link farming is a way to increase relevant incoming links to your website. The purpose of use this tactic is link popularity to increase the Google PageRank. A link farm can be a website or a group of websites having a large number of outgoing links other sites without any relevant categorization.
Linkbaiting is the practice of crafting content that is designed to get other content producers to link to it. The purpose is increasing the number of inbound links to your content and thus improving its performance in search engine results.