A program, similar to telnet, used to connect to remote IBM mainframe hosts, many of which do not understand telnet. The program emulates a 3270-type terminal.

For many tn3270 versions, the "clear screen" function is activated by typing Control-Z. When logged on to an IBM host and "HOLDING" or "MORE..." appears at the lower right corner of the screen, the "clear screen" function must be entered to display the next screen. tn3270 emulations usually include function key definitions.