The complete eradication of an idea, behavior, belief or ideology from the public consciousness, to the point where it can no longer be taught to newpeople. "To kill an idea".
Although banning Holocaust denial from social media platforms will likely reduce the influence of that particular toxic idea, as long as people are still able to discuss it in private or public forums, it is a far cry from true memecide.
The ideational equivalent of genocide. A meme is an idea. Memes are to cultural evolution what genes are to biological evolution, any idea that spreads or doesn't dependent upon culture's evolutionary process. Memocide therefore is any sort of absolute-faith-based fundamentalism, a holy war to eradicate from culture all traces of an idea considered evil by someone whose confidence level in a countervailing idea reaches 100%.
Did my folks like my punk music? Are you kidding? Their response was memocide. If they could, they would have eradicated punk not just from our house but from the universe!
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).