It's a new address format for Bitcoin Cash proposed by BitPay, to prevent BTC/BCC address confusion. It's not widely used, currently.

- The old addresses that start with `1` (P2PKH) are converted to addresses that start with `C`

- The old addresses that start with `3` (P2SH) are converted to addresses that start with `H`

References:

BitPay blog post: https://support.bitpay.com/hc/en-us/articles/115004671663-BitPay-s-Adopted-Conventions-for-Bitcoin-Cash-Addresses-URIs-and-Payment-Requests

BitPay address translator: https://bitpay.github.io/address-translator/