ZMP, the Zenith MUD Protocol, is a command protocol designed to operate within a telnet stream. The purpose of ZMP is to allow for advanced communication between a MUD server and client. Similar protocols include MXP and MCP.
Unlike alternative MUD protocols, ZMP does not define a new encapsulation mechanism for transmitting ZMP commands. ZMP utilizes the telnet sub-request facility and option negotiation to encapsulate its command protocol. This quality greatly reduces the complexity of implementing the protocol. It also avoids the complexity of the security mechanisms other protocols employ to prevent users from maliciously injecting protocol commands.
For more information on ZMP, review the specification.