Pay to Anchor (P2A).

Would define Pay to Anchor, a tiny output anyone can spend, used as a hook for adding fees to a payment later.

Systems such as Lightning sign payments before the right fee is known. An anchor output lets someone later attach a child payment that adds fees. It needs no key or signature, which keeps it small, and should be paired with BIP 431. The BIP says Bitcoin Core already relays payments that spend these outputs.