A weblink city is a web page (or a record of websites) developed only for the purpose of helping the weblink developing of another site by helping the number of incoming inbound links. A weblink city usually looks like a regular web page, but many of the material is inbound links -- often exclusive and unrelated -- to other websites. Regard....
Link farm means generating lots of backlinks. It is considered basically as a spam activities. We must do linkbuilding activities and getting the best backlinks from high quality and high page rank sites.
Link Farm means you are buying backlinks from Artificial Sites. Link Farms made by expired domain cause that sites have good domain age and High PR but that's unnatural thing cause Google never consider "UNNATURAL LINKS". Its chances to getting penalized. It calls "Black Hat SEO" tactics. You can rank overnight by using Link Farms but its harmful for your website. SEO is not a magic to get in rank overnight.
A page or a site which contain too many unnecessary links on it pointing to other web sites or pages. People make link farms in order to get a backlink but a back link like these are worth nothing. It is called irrelevant method because on a link farm you will see link too almost sites of any niche hence there is no concept of reletavity in it...