DNS and Service Discovery.
CoreDNS is a DNS server. It is written in Go. It can be used in a multitude of environments because of its flexibility.
CoreDNS is a DNS server/forwarder, written in Go, that chains plugins. Each plugin performs a (DNS) function.
CoreDNS can listen for DNS requests coming in over UDP/TCP (go'old DNS), TLS (RFC 7858), also called DoT, DNS over HTTP/2 - DoH - (RFC 8484) and gRPC (not a standard).