A query is the binary DNS wire format sent with POST or base64url-encoded in a GET parameter named dns to a URL such as https://cloudflare-dns.com/dns-query or https://dns.google/dns-query; several providers also offer a JSON API. Browsers use DoH for name resolution when configured or when the system resolver supports it; DNS over TLS (RFC 7858, port 853) and DNS over QUIC (RFC 9250) are the alternatives.
DoH encrypts the path to the resolver but does not authenticate the data the way DNSSEC does, and the resolver still sees every query. For tools, DoH is a convenient way to fetch public records (CAA, TLSA, DNSKEY, TXT for DKIM and DMARC) from a browser; this site's server-assisted DNS checks fetch only public names this way.