Welcome to Over50sForum! The site for people over 50 to chat, make friends, discuss, share, and generally be part of something that's fun and friendly :)
I still haven't worked out what a meme is..........
As Tiff says, it's a funny picture or cartoon with an amusing caption that once posted on a particular site or media platform such as Twitter or Facebook page, or indeed OFF, it is copied and posted on to other sites or Facebook pages and thus spreads itself. (Not unlike a virus in that respect).
Speaking of viruses (clumsy segue) here's one I nicked from another site ...