The New World is a term that describes the setting of the Destroyermen book series.
The New World is an alternate reality (parallel dimension) that acts as a relay for a varying number of 'Old Worlds'.
This World is going through an ice age. As such its seas and oceans are lower then the Destroyermen's old world, causing more land to be exposed. The major differences in the New World's lands from the Old, is most noticeable in the shape of it's lands.
This is further described on "The Squall" page.