The Fibonacci spiral is a spiral curve that expands based on the Fibonacci sequence, where each number is the sum of the two preceding ones. To construct the spiral, draw a line segment with length F1 units, then draw another segment at a 90 degree angle with length F2 units, and continue drawing new segments at 90 degree angles with lengths F3, F4 and so on, where Fn is the nth term in the Fibonacci sequence. The result is a spiral curve that approximates the golden spiral found in nature.