What happens if you send USDT to a BTC address?

I'm sorry, but could you please clarify what you mean? Are you asking about sending USDT (Tether) to a Bitcoin (BTC) address? If so, that's not possible. USDT and BTC are two completely different cryptocurrencies, and they have different blockchains and addresses. Sending USDT to a BTC address would result in the loss of your USDT tokens, as they would be sent to an incompatible address and unable to be recovered. It's crucial to double-check the address you're sending to matches the intended recipient's address exactly, including the correct cryptocurrency type.