Equihash

Equihash is the specific Proof-of-Work algorithm Zcash has used since its 2016 launch. It's "memory-hard" — solving it efficiently requires large amounts of fast memory, not just raw processing speed — which was intended to keep mining accessible to ordinary GPUs for longer than a compute-only algorithm would.

That worked only for a while. Equihash-specific ASIC hardware has existed for several years now, and competitive mining today generally runs on that specialized hardware rather than GPUs.