Link Farm
A link farm is a website, or a network of them, built for no purpose other than holding links. Nobody reads these pages. No editor chose to include anyone. A machine generated the site and a machine put your name on it, and that is the whole arrangement. It is what you actually receive when you buy five thousand backlinks for forty dollars.
The warning most people have absorbed about this is out of date, and the current truth is more useful. For years Google actively punished sites with obviously purchased link profiles, and a great many businesses were badly hurt. Then the systems became good enough at recognising the pattern that punishment stopped being necessary. Now the links are mostly just ignored.
That changes the honest objection. Buying links is not primarily dangerous; it is a purchase of nothing. The dashboard fills, the number rises, and no effect follows, because the thing being counted was never the thing that worked. What a search engine is trying to detect is a human decision — somebody read something and judged it worth pointing their readers toward. A farm reproduces the visible artefact of that decision with the decision removed.
The test is simple enough to apply without any tools. Did a person exercise judgement in placing this link? Would its readers plausibly want what you offer? Would you want the link at all if search engines did not exist? A link that fails all three is a decoration, and decorations do not compound.
The human translation is a wall of framed certificates that anyone could have printed. The frames are real. The wall is full. Nobody is impressed, least of all the people whose job is to notice.