Dbref

Some articles on dbref:

MUF (programming Language) - The MUF Stack
... That is, the primitive requires a string to be on top of the stack, with a dbref immediately below that ... If player Alice had a dbref of #99, then the code #99 "Hello there!" notify...would output the string "Hello there!" to Alice's screen ... If the program did not have a dbref and a string on the top of the stack at runtime, in this order, the program would crash ...
MUF (programming Language) - Hello, World
... "me" is a variable it holds the dbref of the user running the program ... the value stored in the variable "me" (the user's dbref), and puts it on the stack ... After this statement, the string will be put on the stack (above the user's dbref) ...