Wood is gathered from trees. Different trees yield different base amounts, ranging from 1 to 5.
You can boost the overall yield in several ways. One is to boost your Perception using food (Grilled Carrots are the most accessible) which gives you a chance of getting the equivalent of an extra hand harvest on that tree, with no increase on the regen timer. Another is to use a Hatchet, which can multiply the yield (and the regen timer) by 1 to 5, depending on the quality (and some luck).