There are many spies in the land, and various methods of 'bugging' your conversations - including, most commonly, the use of the bug-shaped rune. This will allow others to eavesdrop on your private tells but can be negated by seeking out the so-called privacy locations. These are locations in which, when you LOOK at the verbose description, you will see the 'there is a distinct feeling of privacy here'. In such locations you will be COMPLETELY private, impossible to bug or eavesdrop by any means, mortal or divine. In privacy locations you can type PEER at any time and even hidden, invisible or divinely concealed people will be revealed to you.
See: HELP SPEAKING for the main help-file on forms of communication, with HELP COMMUNICATION the non-beginner summary; HELP CALLING with details of calling channels and HELP SAY, HELP SHOUTING and HELP ADVICE for specifics on various ways to make yourself heard.