This is the GNS-430W, a newer and much-improved version of the popular GNS-430. There are a number of improvements in the GNS-430W, but the primary ones are WAAS Approach Capability and Terrain Information.
WAAS, or Wide Area Augmentation System, is a fundamental improvement to GPS accuracy. By adding a series of ground stations and geostationary satellites, WAAS GPS is typically 5 times more accurate than "regular" GPS. This means that it is now possible to fly a complete "Virtual Glideslope" approach into an airport with no local ground-based navigation aids whatsoever. A GNS-430W makes the following approaches available.
LNAV (Lateral Navigation): This is a new name for non-precision GPS approaches as we have known them. Like all non-precision approaches, this has a minimum descent altitude (MDA), based on obstructions and terrain.
LNAV/VNAV (Lateral Navigation / Vertical Navigation): This class of approach provides Glideslope vertical guidance with a decision altitude and others