It determines what can and cant be installed in an area prone to getting wet. For example, a switchboard cant be installed in a wet area but lights can be installed in wet areas if they are of an appropriate IP rating for dampness or extra low voltage.
Wet areas are classified into zones. If we take a bath as an example. Zone zero is inside the bath, zone one is directly vertical and adjacent to zone zero.
Zone three is directly vertical and adjacent to zone two. Different rules for lights, power points, and switches exist for each zone.
