What it means
You give Meta or Google a seed audience — purchasers, high-LTV customers, qualified leads — and the platform models millions of similar users to target. The quality of the output depends entirely on the quality of the seed.
Why it matters
Lookalikes are the bridge between your first-party data and cold reach. Seed them with your best customers (high LTV, not just any buyer), keep seeds fresh, and they consistently outperform broad interest targeting. Feed a weak seed and you scale your worst customers.