Just earlier terms for warp and weft. Ends are the same as warp: the threads run vertical, top to bottom. Picks are the "fill" threads, same as weft: they run horizontal, side to side. I don't know what M stands for. But our modern term for "end on end" fabric is actually a bastardization of "end and end," which meant threads of alternating colors, side by side, that run top to bottom. As always, I could be wrong, but I think that's a close definition.