Definition of Chain Spam

Chain spam is a tx on the blockchain containing data such as text, pics, audio, or video. A tx on the blockchain is not spam if, in as few bytes as possible, it does one of only two things, and nothing else: (1) transfers value on L1 or (2) sweeps funds from an HTLC or similar address created while trying to transfer value on an L2. The term "value" means the "value" field in L1 BTC utxos, and "transferring" it means reducing the amount in that field in the sender's utxos and increasing it in the recipient's utxos.