Strickly speaking no. A link farm would be a page/site that consists only of links. The links are not sorted in any way or have any relevance to each other. A directory is a sorted collection of links in different categories. Most directories are very strict about they sites they allow and over value to visitors by making it easy to find relevant links (sites). However some directories could be viewed as link farms. It's always good to keep the quality of the directories you submit to in mind. If it doesn't look trustworthy or useful to visitors, it's best to stay away.
Also, good directories are human edited, whereas a link farm is not. That and the categorization are the two main distinctions.
judging by the amount of crap adsense sites in my directory, by a mathematical algorithm, i come close (but for sure not over the %) to a "link farm" ... adding the fact that i manually reviewed all this sites and rated them 1 (lowwest) makes my directory better than dmoz (but anywhay is easy to be better than dmoz ) so a "link farm" is what Google algorithm + Google human intervention think it is : atm a link farm is a net of pages which contains only links that point one to eachother in a vicious circle. next pr & back link update will tell what the new definition is
Link farm are pages that have 100+ outcoming links, without any additional content. Directories are not link farms, but they don't help so much as links from content pages do.
No , because directories have uniq content... i mean uniq content as a whole... a website can be in yahoo/google/msn ... but the google serps is uniq, and same yahoo database... links farms, are usualy dublicated content (as a whole) links farms are "web directories" copy & pasted into hudrentds or even thousants of websites around the internet@