An ASIC (application-specific integrated circuit) miner is a device specialised only for a specific type of work. In cryptocurrency space, the ASICs are capable to hash certain mining algorithms (i.e. SHA-256 on Bitcoin or Equihash on Zcash) with high efficiency.
These workers represent an upgrade to CPU/GPU chips mining which usually become obsolete for mining after the ASICs are developed and introduced to the market.
Visit asicminervalue.com for a comprehensive list of ASIC miners for different coins.