stETH holders are users whose Ether is staked through Lido and who hold stETH tokens representing their staked ETH

Quotes that support claims

In the new paradigm, Lido stakers (those who hold stETH tokens) will be able to register dissent against DAO proposals by depositing stETH into an escrow contract. If at least 1% of Lido’s total staked ETH is deposited in the escrow by dissenting stETH holders, the proposal is delayed for an initial period of 5 days, with the time delay increasing as more stETH tokens are deposited.

If approved, the proposal will activate a new framework that gives stETH holders — users whose ether is staked via Lido — a formal mechanism to delay or veto governance actions, adding a novel layer of accountability to the voting system. The new technical mechanism has implications for all of crypto, not just Lido, according to the prominent albeit pseudonymous researcher and advisor Hasu.“Lido really reduces the risk that users have from any kind of governance attack [and] the trust that they need in the maintainer companies and the LDO holders,” Hasu told Blockworks.