Trustline
A trustline is a Stellar account’s explicit opt-in to hold a specific asset, such as USDC from a specific issuer. Each trustline reserves 0.5 XLM while it exists, and until the trustline is added the account cannot receive that asset at all. Adding one takes seconds in any Stellar wallet.
A trustline tells the Stellar network “this account accepts this asset from this issuer.” It is Stellar’s built-in spam defense: nobody can fill your wallet with tokens you never asked for. The practical consequence is a one-time setup step — before receiving USDC, PT, or YT, your wallet must add the matching trustline, which reserves 0.5 XLM until removed.
Because anyone can issue an asset with any ticker, the trustline is also where you verify the issuer. The real USDC is issued by Circle; wallets mark it as verified. Checking once, when you add the line, protects every transfer after it.