DB-25
D-Sub-9 or D-Sub-25
DB-25 D-Sub-9 or D-Sub-25
DB9 is a connector, not a cable. It is most commonly used for RS-232 serial connections like an external modem.
RS-232
The 232 doesn't stand or come from anywhere. It's just a reference number. RS-232 = Recommended Standard 232
Recommended Standard 232
You need to get a Bluetooth RS-232 dongle, which connects to serial RS-232 port and provides bluetooth connectivity. These are similar to USB bluetooth devices to some extent, but need a power source for the electronics circuitry (as you may be aware that USB ports have 5V power supply but RS-232 standard has no option for power supply on the connector). So Serial port to Bluetooth convertors will have either an inbuilt battery or a power supply connector to feed power. Here are examples : http://www.lemosint.com/scripts/bluetooth_parani_sd.asp http://serialio.com/products/adaptors/BlueSnapXP.php - Neeraj Sharma
onion
The standard defines the voltage levels that represent logic levels on the line.It doesn't specify a connector. DB-9, 15, and 25 are among the popular ones,but RS-232 circuits can even be wired directly, through 3 or 4 leads, withouta connector, and without violating anything in the standard.Moreover, we should at all times remain mindful of the immortal words of the giantsupon whose shoulders we all stand:"The best thing about standards is that there are so many good ones to choose from."
it is cable used for data transmission between computers
The RS 232 interface is one of the standards used in serial communications. It uses serial signals (as opposed to parallel) to connect computers to devices like printers and modems.
power meter
RS-232 is a Recommeded Standard (RS) for serial communications. It can be both input and output, or just one or the other. There are RS-232 devices called DCE (for Data Communications Equipment) like a printer, modem, mouse, joystick, monitor. There are RS-232 devices called DTE (for Data Terminal Equipment) like a notebook computer or tower. Two computers may talk to each other over an RS-232 link. The "boss" computer would be the DTE; the "slave" computer would be the DCE. {In practice, nobody really uses RS-232 for intra-computer linking in home or office, but it might be used for fairly long connections on, say, an antenna farm if fiber optics is unaffordable.}