White tea is considered the most natural tea, as it is not heated at the same high temperature as green tea. The taste varies from extremely light (like Silver Needle) to more complex (Bai Mudan). White tea gets its name from the white color of the buds used to make the tea. The leaves and/or buds are preferably dried outdoors or indoors at 30 degrees (sometimes warmer). They are not roasted/fried or steamed as green tea is, and are therefore considered more sensitive to moisture.
Like green tea - and black for that matter - it comes from the tea bush and contains caffeine.