The Quote of the Day (QOTD) service is a member of the Internet protocol suite, defined in RFC 865. As indicated there, the QOTD concept predated the specification, when QOTD was used by mainframe sysadmins to broadcast a daily quote on request by a user. It was then formally codified both for prior purposes as well as for testing and measurement purposes in RFC 865.
A host may connect to a server that supports the RFC 865 QOTD protocol, on either TCP or UDP port 17. In order to keep the quotes at a reasonable length, RFC 865 specified a maximum length of 512 characters for the quote.
Although some sources indicate that the QOTD service is rarely enabled, and is in any case often firewalled to avoid 'pingpong' attacks, interest continues in the pre-existing purpose of serving quotes as can be seen with web engine searches.
Current testing and measurement of IP networks is more commonly done with ping and traceroute, which are more robust adaptations of the echo protocol (RFC 862), which predated the attempt at QOTD standardization.