The Fibonacci sequence is a series of numbers in which each number is the sum of the two preceding numbers: 0, 1, 1, 2, 3, 5, 8, 13, and so on. This sequence appears in many natural patterns, such as the arrangement of leaves on a stem, the branching of trees, and the flowering of artichokes. In fact, the Fibonacci sequence is so ubiquitous in nature that it's often referred to as "nature's code."