Which type of growth is defined as lateral growth?

Lateral growth refers to the increase in thickness or girth of an organism, particularly in plants. This type of growth is primarily facilitated by the activity of the lateral meristems, notably the vascular cambium and cork cambium, which produce new layers of vascular tissue and protective bark, respectively. This allows the plant to expand outward, enhancing its structural support and stability.

In contrast, growth that results in an increase in length typically refers to primary growth that occurs at the tips of roots and stems, while leaf development is associated with other processes that do not inherently involve lateral growth. Therefore, the definition provided aligns precisely with the concept of lateral growth, making it the correct choice.