These are the famous 1602 16x2, 2004 20x4 and 1604 16x4 LCD Modules.
The 1602 16x2 module displays 2 character rows consisting of 16 characters each.
The 1604 16x4 module displays 4 character rows consisting of 16 characters each (no backlight on the green/yellow version of this display)
The 2004 20x4 module displays 4 character rows consisting of 20 characters each.
Optional I2C module.
These are commonly used in Arduino, MSP430 and other microcontroller projects by enthusiasts as well as being used commercially in copiers, fax machines, printers, industrial test equipment, networking equipment and many other types of devices.
Choose from two colour variants:
- white characters on blue background and backlit
- black characters on green/yellow background and backlit (no backlight on the 1604 green/yellow)
2004 and 1602 boards are now available with an I2C adapter soldered on.
There is a handy Arduino tutorial here:
https://www.instructables.com/id/Quick-Setup-Guide-to-Arduino-LCD-2004-With-PCF8574/
And a handy I2C scanner here:
http://playground.arduino.cc/Main/I2cScanner