Short answer
Mint authority is the permission to create new units of a token. If it hasn't been revoked, whoever holds it can print supply and dilute every holder.
Every Solana token has a mint account with an optional mint authority. While that authority exists, its holder can issue more tokens whenever they like. For a memecoin with a fixed story, that's a lever nobody needs.
If the creator keeps it, they could mint a huge amount and sell it into the pool, crashing the price. Revoking it (setting it to none) is permanent and visible on-chain, which is why it's one of the first things to check.
A revoked mint authority is necessary but not sufficient. Insiders can still dump tokens they already hold, so look at holder concentration too.
See the checks for yourself
18+ only. Self-custodial: you keep your keys. 0.5% per trade, no minimum. Memecoins can go to zero.