Spamdexing
Spamdexing is tricking a search engine into ranking pages higher than they deserve, through tricks like keyword stuffing, hidden text and link schemes.
Spamdexing is the old name for tricking a search engine's index: getting pages to rank higher than they deserve through methods that break the search engine's rules. The word joins spam and indexing. Today most people just call it search spam or webspam, but it means the same thing.
It matters to a marketer for two reasons. Doing it can get your site demoted or removed. And a competitor's spam can crowd you out of results until the search engine catches up.
Common tricks
The classic methods work on the words or on the links. On the words: stuffing a page with keywords, hiding text in the same colour as the background, showing search engines one page and visitors another, or churning out thousands of near-empty pages. On the links: buying them, swapping them, or building networks of sites that only exist to link to each other.
Google lists what it treats as spam in its spam policies, and runs automated systems to catch it, along with manual actions by its staff.
For example, a coffee shop that fills its footer with "best coffee Leeds coffee shop Leeds cheap coffee Leeds" in white text is spamdexing. Google is very good at spotting that one, so it's more likely to hurt than help.
The AI version
The same urge now aims at AI answers. People publish pages that state their brand is the best, plant hidden instructions for AI models in a page, or flood forums with fake recommendations, hoping an AI platform will repeat them. Some of this works for a while. AI platforms and search engines are learning to spot it, and a brand caught doing it risks the trust it was trying to win.