Originální popis anglicky: 
ttytype - terminal device to default terminal type mapping
The 
/etc/ttytype file associates termcap/terminfo terminal type names
  with tty lines. Each line consists of a terminal type, followed by whitespace,
  followed by a tty name (a device name without the 
/dev/) prefix.
 
This association is used by the program 
tset(1) to set the environment
  variable TERM to the default terminal name for the user's current tty.
 
This facility was designed for a traditional time-sharing environment featuring
  character-cell terminals hardwired to a Unix minicomputer. It is little used
  on modern workstation and personal Unixes.
A typical 
/etc/ttytype is:
 
con80x25 tty1
 
vt320 ttys0
 
 
  - /etc/ttytype
- the tty definitions file.
getty(1), 
termcap(5), 
terminfo(5)