An application-specific integrated circuit (ASIC) is a chip customized for mining, rather than intended for general-purpose use (such as GPU). Such a device may provide much better mining performance than GPU.
The Bitmain Antminer S9 (11.5Th) was produced by Bitmain and released in 2016. This miner consumes 1127W, producing 11.5 Th/s of hashrate with the sha-256 algorithm, which makes this device almost (if not at all) useless. We do not recommend buying this device for mining nowadays.