Pressure-treated wood is lumber that has been infused with chemical preservatives to protect it from rot, insects, and other forms of decay. This process involves placing the wood in a large chamber where air is removed, allowing the preservatives to penetrate deeply into the wood fibers. This type of wood is commonly used for outdoor projects, such as decks, fences, and garden beds, due to its enhanced durability. However, it is important to handle it with care, as the chemicals used in the treatment can be harmful if ingested or improperly disposed of.