Hideo Kojima has been talking up his mysterious "Project Ogre" at Twitter for the past year. In Japanese, he refers to the project as "Oni Project." Today, he clarified what the "Oni" means.
There have been a few theories of what the Oni might mean. Perhaps this is such a big project that it's devilish or demonic. Or perhaps it's a game that requires Kojima to close off his heart as he makes it (this is from a proverb involving Oni, I believe).
These two are both incorrect, said Kojima at Twitter today. The meaning is more literal. Oni Project is a game that deals with Oni in some capacity.
Oni can be translated to a variety of things, including demon, devil, and, of course, ogre. Based off Kojima's Tweets, it's unclear if he's saying that the game deals with Oni as a subject matter, or if it's the player who handles Oni in some form (collecting spirits and so-forth).
So Project Ogre/Oni Project is still a mystery. But perhaps you can find some clues to its nature by looking carefully at the bento Kojima had during a lunch meeting discussing the game today.