Fourfold means four times as much, or having four parts. If something increases fourfold, it becomes four times larger than it was before. When a baker quadruples a recipe, making four times as many cookies as the original instructions called for, the ingredients increase fourfold.

The word can describe multiplication: if your school's robotics club had 5 members last year and has 20 members this year, membership has grown fourfold. It can also describe something with four distinct parts or aspects, like a fourfold plan that includes four separate steps to solve a problem.

You might hear about fourfold growth in technology, where computer processing power becomes four times faster, or fourfold improvements in athletic performance. When something increases twofold, it doubles. When it increases threefold, it triples. When it increases fourfold, it quadruples.