A live oak is an oak tree with evergreen characteristics, retaining its foliage year-round rather than dropping its leaves in the fall. The term “live oak” is mostly used in North America, causing people to associate the live oak specifically with the American South and Southwest, but in fact evergreen oaks also appear in Europe and Asia, though they are not known as live oaks in these regions. In the South especially, the live oak is an iconic symbol; the State Tree of Georgia, for example, is a live oak.
All live oaks are in the genus Quercus, and they are evergreen, but beyond that, they don't share many traits. They can be found in several different groupings within their parent genus, and they vary widely in shape and size, producing a range of styles of leaf, as well. Like all oaks, live oaks produce acorns for reproduction, and they have famously strong wood which can be used for a variety of building tasks.
The “live” in “live oak” is a reference to the fact that the trees look alive, even through the dead of winter. Deciduous trees tend to look rather disreputable after they lose their leaves, causing the landscape to look rather dead and bleak, but evergreens stay green through the winter, injecting a bit of color into the winter landscape. Especially for new settlers facing unfamiliar sights in the Americas, the live oak was undoubtedly a pleasant sight during harsh winters, as a reminder that spring would eventually arrive.
Live oaks are also known as encinas, in some regions, and several American cities are named “Encina,” or “Live Oak,” presumably in a reference to a large number of these trees. The trees can live for up to 300 years when allowed to grow unmolested, developing very strong, healthy timber and abundant low-hanging branches like other members of the oak genus. Live oaks have been used for thousands of years all over the world for their sturdy timber, which was especially vital in American shipbuilding.
Many live oaks provide habitat for epiphytic plants, plants which grow on other living species rather than rooting into the ground. Spanish moss in the South is a famous example of an epiphytic plant, but mistletoe and a variety of other plants can be seen colonizing live oaks as well. Live oaks are often cultivated for their ornamental foliage, in which case the epiphytic visitors are either a bonus or a nuisance, depending on one's point of view.