To help with clarity and a common understanding, here are some helpful terms and their definitions.
Superchain member: A chain with an agreement in place to commit sequencer revenue back to the Optimism Collective.
Blockspace charter: A Blockspace Charter is a technical-focused governing document (and framework) for the Superchain.
Standard chain: A chain that conform to the Standard Rollup Charter - not ratified yet
Frontier chain: A non-standard chain which has modifications that do not fit the Standard Rollup Charter criteria.
Standard chain candidate: A chain that has met most of the standard chain criteria, except for the ProxyAdminOwner key handover.
Key handover: A colloquial term for updating the chain's ProxyAdminOwner to fulfill the requirements from the standard rollup charter.
Chains in the superchain-registry are assigned a superchain_level (shown in individual config files as well as the chainList.toml/json summaries), depending on the set of validation checks that they pass.
Frontier chains have superchain_level = 0.
Standard chains have superchain_level = 1. Because they satisfy a much stricter set of validation checks (see the Standard Rollup Blockspace Charter), they also qualify as Stage 1 rollups chains.