Marris Otter is a specific cultivar of two row malting barley owned by... I want to say Warminster Maltings in the UK. it's grown by a bunch of farmers. While standard '2 row' is any of several cultivars of 2 row barley grown all over the world. Marris Otter, Optic, Golden Promise. These are other 'named' varieties from the UK.
Some MO is floor malted which means that instead of being malted in a big temp/humidity controlled drum that constantly turns it and keeps the moisture and temp exactly right, it is malted the 'old fashioned' way, spread out on a floor and moved by hand (or mechanized rake) as it moved through the malting process.
It is also often kilned to a slightly higher color than 'normal 2-row' and is reputed to have a fuller maltier flavour.
The name I can't speak to. I imagine the breeder that came up with the cultivar had a reason for it.