The Marshall Mather "LP"

Just what exactly does LP stand for, i’ve seen this in other albums too. I’ve also seen EP at the end of record titles as well, What is this shit?

It’s always been my understanding that and EP was an ‘extended play’ or ‘extra play’ because it wasn’t a ‘full album’ and usually a little cheaper. Digital Underground (brought us The Humpty Dance) released an EP not too long after ‘Sex Packets’ (Humpty Dance.) It only had about half the songs an LP would have.
LP, I thought, meant Long Play.

I could be wrong about all this, but that’s my view.