KYC (Know Your Customer)
KYC stands for Know Your Customer and it's the identity verification process that licensed online casinos are legally required to perform. Before they send you money, they need to confirm you are who you say you are. This means submitting documents: a government-issued photo ID (passport or driver's licence), proof of address (utility bill or bank statement from the last 3 months), and sometimes proof of payment method (screenshot of e-wallet or photo of the card you deposited with).
Most casinos will let you deposit and play without completing KYC, but they'll block your first withdrawal until verification is done. The review process takes anywhere from a few hours to 72 hours depending on the casino. Some casinos are infamous for dragging it out with repeated document requests.
Pro tip: complete your KYC immediately after registering, before you even start playing. That way, when you hit a win and want to cash out, there's no waiting. Submitting documents after a big win feels more stressful than it needs to be, and some players have reported more scrutiny on larger withdrawal amounts.