A DNS query is a request for information from a DNS server.
For example, each time you enter a domain name into your browser, such as example.com, your browser make a DNS query to locate the IP address for that domain name. DNS queries traverse a system of ISP caching servers and DNS servers to locate and return the DNS records for a domain.
Queries can come from user browsers, email security verifications (via SPF and DKIM records), and other automated processes across the internet.