Terminal is a String property that contains the terminal identification string used to identify the terminal type in TELNET suboption negotiations. 

The terminal type information is an NVT ASCII string with a maximum length of 40 characters, as described in the Internet Standards document: 

RFC 1700 - Assigned Numbers  

Please note that Indy does not provide terminal emulation other than a dumb terminal NVT implementation as indicated by the value 'dumb'. Any non-null string value can be used in Terminal, but requires handling terminal and data emulation manually.