succinct serial port line definitions

courtesy of Google Definitions:
DCE:
Data communications equipment (modem)

DTE:
Data terminal equipment (computer)


DSR:
An RS-232 modem interface control signal (sent from the modem to the DTE on pin 6) which indicates that the modem is connected to the telephone circuit. Usually a prerequisite to the DTE issuing RTS.
www.marconi.com/html/glossary/glossaryd.htm

DTR:
An RS232 modem interface control signal (sent from the DTE to the modem on pin 20) which indicates that the DTE is ready for data transmission and which requests that the modem be connected to the telephone circuit.
www.marconi.com/html/glossary/glossaryd.htm

CTS:
Clear To Send: When using DCE (Data Communications Equipment; a modem is a common example), the CTS indicates that the DCE is ready to accept data.
www.uic.edu/depts/accc/inform/v106a.html