ASIC miners are devices that are purpose-built to mine cryptocurrencies. They are much more efficient than regular CPUs and GPUs, which is why they are often used by large-scale miners.
However, ASIC miners can only be used to mine a specific coin or algorithm, so they are not versatile like GPUs.
There are currently no ASIC miners available for Ethereum. This is because Ethereum uses a different mining algorithm than Bitcoin, called Ethash.
Ethash is designed to be ASIC-resistant, meaning that it is very difficult to create an ASIC that can mine Ethereum efficiently.
However, this doesn’t mean that ASICs will never be developed for Ethereum. If Ethereum becomes more popular and its price increases, there will be a greater incentive for companies to develop ASICs for it.
For now, though, Ethereum mining remains mostly decentralized, as it is meant to be.