Holder concentration is how much of a token's supply is owned by a small number of wallets. When a few big holders control most of the supply, the project is riskier because they could dump their tokens and crash the price anytime. You can check holder distribution on block explorers like Solscan or Etherscan by looking at the token's page—it shows you the top 10, top 100, and top 1000 holders as percentages. If the top 10 holders own more than 50% of the supply, that's a red flag worth paying attention to. Another useful metric is looking at the team and investor allocations in the tokenomics. Vested tokens that unlock over time can create selling pressure, so read the vesting schedule. Don't let a small flock of whales be the only ones roosting on your investment thesis. Diversified holder bases tend to be more stable than concentrated ones, though this alone doesn't guarantee a project's success.