Search engine spam or search spam is a method that deliberately uses to manipulate the index of search engines. There are many sorts of methods can be used to accomplish the spam indexing system. It is a black hat technique used in web spamming activities.
And the link farm is a developing of the link within the group to all other sites in the group. It can be created by hand but mostly works by an automated program. The link exchange program is something that distributes and exchanges the values between sites. The link farm is different from it and so can be understood as one-way links coming directly to a single site.

Link farm is a basic method of other SEOs in which they generate different websites to pass every link that they want to rank in the search engine.