Glossary
Data Availability Committee
A permissioned group of parties that stores a Layer-2's off-chain transaction data and attests to its availability, letting validiums and optimiums scale without posting data to L1.
A Data Availability Committee (DAC) is a fixed set of trusted members that hold a copy of a rollup's transaction data off-chain and sign attestations confirming they have it. These signatures are checked on L1 before state updates are accepted, giving users a guarantee that the data needed to reconstruct balances and exit the chain actually exists somewhere.
DACs power validiums and optimiums — designs that keep data off-chain to cut costs far below a normal rollup. The trade-off is a weaker, trust-based availability assumption: if a threshold of members collude or go offline, the data can be withheld and withdrawals may stall. StarkEx-based chains such as Immutable X and earlier dYdX relied on DACs, and many appchains use them as a cheaper alternative to posting every byte to Ethereum or a dedicated DA layer like Celestia or EigenDA.