The Item Buffer is a block added by Ender IO. It is used as a buffer for items. It has a 3x3 inventory space, for a total of 27 stacks of items.
Right Clicking on the Item Buffer will open its GUI. The Item Buffer GUI lets you assign each face with a status of Push, Pull, Push/Pull, Disabled or None. The Item Buffer can also be controlled by Redstone with states active with signal, active without signal, always active, never active.