Unix uses the TERM environment variable to look up various escape sequences in the termcap database to allow programs to do more than just output characters to the terminal (which in these days typically are emulated in CMD.EXE, Putty or similar). Examples are "clear the screen", "move cursor to a specific spot on the screen".
Your terminal emulator is configured to tell Unix that it emulates "term-256color" but Unix does not have that terminal in its termcap database.
Reconfigure your terminal emulator to tell that it is one that it knows. Typical examples are "vt100" and "xterm". Which one exactly may require some experimentation after close reading of the documentation.