The datasheets that are provided for electronic components are terse and often cryptic. The application notes that are sometimes available are somewhat better in this regard, but not much. Unfortunately the examples provided with the Arduino follow this same pattern.
Here's the comment at the beginning of the sketch: Demonstrates the use a 16x2 LCD display. The LiquidCrystal
library works with all LCD displays that are compatible with the
Hitachi HD44780 driver. There are many of them out there, and you
can usually tell them by the 16-pin interface.
This sketch displays text sent over the serial port
(e.g. from the Serial Monitor) on an attached LCD.
The first (cryptic) paragraph tells you that the LCD interface is the standard parallel one and the second (terse and cryptic) paragraph tells you that the source of the information to be displayed on the LCD comes in via the Rx pin and uses the USART in the ATmega, frequently via the USB cable. Remember that USART stands for Universal Synchronous and Asynchronous serial
Receiver and Transmitter and USB stands for Universal Serial
file -> examples -> liquidcrystal -> serial display
Thus 'serial display' is an unfortunate choice for the folder and sketch name since the term 'serial' refers to the source of the data that is being displayed on the LCD rather than the type of interface to the LCD.
PS Did you notice how the sketch cleverly avoids any reference to the R/W pin on the LCD?