A catalyst is something that makes a change happen faster or causes something important to begin. In chemistry, a catalyst is a substance that speeds up a chemical reaction without being used up itself. For example, enzymes in your body are catalysts that help break down food quickly enough for your body to use it. Without these catalysts, digestion would take days instead of hours.

Outside of science, we use catalyst to describe anything that sparks change or gets things moving. A new student might be the catalyst for your friend group trying different activities. A teacher's encouragement could be the catalyst that makes you finally start writing that story you've been thinking about. An invention like the printing press was a catalyst for spreading knowledge across Europe.

The key idea is that a catalyst doesn't just participate in change. It triggers or accelerates it. When historians say an event was the catalyst for a war, they mean it set everything in motion, even if other problems had been building for years. A catalyst is that critical spark or push that transforms possibility into reality.