To burn ether just means to send it to the genesis address. But that address does not work with uniswap so Vether would not have worked properly with uniswap. That's why he changed it to this address. If you convert the address from binary to ascii it just spells "value". It's just an arbitrarily chosen address that no one will ever own. Just like the genesis address. You can read more about that here: https://ethereum.stackexchange.com/questions/52908/who-has-access-to-ethereum-0x0000000000000000000000000000000000000000-address