Does anyone know what this terrain generation algorithm is called? I saw it in two places. One was on YouTube, and the other, on Wikimedia.
In addition to what Pikalek said, it's also known as the Midpoint Displacement algorithm (because you perturb the midpoints of each edge) or Diamond-Square algorithm when working with a square instead of a triangle.
I've seen it referred to as 'fractal subdivision.' In this case, you assign a random height perturbation to the corners of the triangle, subdivided it at the midpoints of the edges & repeat the process over again for each triangle until some threshold is met.