The other, other M is for media, which you can click here to see.
Nintendo released a flood of information about Metroid: Other M today, not the least of which is when it's coming out. The Media Summit press release describes a game that takes place primarily in a side-scrolling perspective, using a sideways Wii Remote, but gives the player the ability to switch to first person at any time and control the game with the pointer. So it's an odd hybrid of old Metroid and Prime.
As these screens reveal, it's also very nice-looking (though it must be said, these screens are from a pre-release version, and at a higher resolution than an actual Wii can display). Other M will be in stores June 27.