I'll tell you what mechanically recovered meat is, but you might wish I hadn't!
When all the identifiable cuts of meat - steak, chops, chicken fillets, etc. - have been removed, everything that's left is put into a centrifuge which is operated at high speed so that all the remaining bits of meat are extracted as a kind of slurry which is then used to make cheap sausages, burgers, etc. Although this can technically be described as 'meat' it will also contain bits of skin and probably other bits that I don't really like to think about too much. Ears and nostrils spring to mind, but I'll leave the rest to your imagination!
I have actually seen this process on a visit to a factory and I've never eaten a cheap processed meat product since.