Short answer: Compound interest means earning interest on both the original amount and the interest already earned. That is why money can grow faster over time.
A fuller explanation: When someone asks "What is compound interest?", they usually want more than a one-sentence definition. They want the direct answer, the reason behind it, and a simple way to remember it.
For money questions, the key is to understand the concept before making decisions with real money. A simple financial idea can have different consequences depending on income, debt, time horizon, taxes, risk tolerance, and local rules. A useful way to apply it is to write the numbers down instead of keeping them vague in your head. Small differences can compound over time, especially with saving, debt, investing, interest rates, and fees. This is general education, not personal financial advice. The practical takeaway is to use the concept to make clearer decisions, then adapt it to your own budget and goals.
Simple example: Imagine explaining it to someone who has heard the phrase before but never really understood it. You would start with the main answer, then add one concrete example, then explain why that example proves the point.
Common mistake: The common mistake is stopping at the short answer. That can be technically correct, but it often leaves out the context that makes the answer useful.
How to remember it: Keep the core idea in one sentence, then attach one example to it. The example makes the answer easier to recall later.
Bottom line: Compound interest means earning interest on both the original amount and the interest already earned. That is why money can grow faster over time. The deeper value is understanding why that answer makes sense and how to apply it in a real situation.