Pressure treatment refers to protecting wood from damage caused by insects, moisture, and decay fungi.
Here is a great summary document put out by the Western Wood Preservers Institute; it’s a summary document describing what IBC says out pressure treating wood: 2006IBC-Aug06.pdf
Below are links to pressure treatment facilities that have informative websites:
Care should be taken by the specifier when choosing a treatment type. Waterborne treatments void the warranty on engineered wood products, but not dimensional lumber.
Catalog hardware can be very costly if the wrong treatment is selected. See the file in the “Hardware” section for more info on treatment and hardware compatibility.