Port 53 is a network port used for communication between a DNS client and server. DNS stands for Domain Name System, which is responsible for resolving human-readable domain names into IP addresses that computers can understand. DNS client applications use the DNS protocol to query and request information from DNS servers, and the server returns the results to the client using the same port. Port 53 is used for both TCP and UDP communication. When a user types a URL into their web browser, the browser first sends a DNS query to a DNS server to translate the domain name into an IP address. The response from the server is sent back to the browser on the same port — port 53.

It is worth noting that some organizations or administrators may choose to run their DNS servers on non-standard ports to bypass firewall restrictions, reduce the likelihood of an attack, or for testing purposes. However, non-standard DNS ports are not widely used and are not recommended for general use, because they can cause compatibility issues and can make it more difficult for other systems to locate and communicate with the DNS server. Additionally, non-standard ports are often seen as security risks because attackers may target these ports as they are usually less monitored by security teams.