Memes are popular jokes or characters in social media. These memes are usually very popular among communities since they are usually inside jokes. Because of strong community, these memecoins usually become successful. Though it should be noted that since they are practically created due to memes, there is no really real purpose behind which makes them driven by hype alone.
There is not much difference technically between traditional crypto and memecoins. Memecoins are just categorized differently due to the idea they represent which are memes.