where is LCD.h

I am trying to install and use an Arduino program onto a system I am building. The author included the statement

#include <LCD.h>

to control a standard LCD with I2C controller.

I can't find this in the Arduino playground, but it appears to be a standard Arduino library.

Does anyone know where I can find this?

What is a "standard" library? One that is bundled with the IDE?
If so LCD.h is from a 3rd party library not from a "standard" library.
LCD.h is part of fm's newLiquidCrystal library.

It cannot be installed using the library manager and must be installed manually.

If that library is installed properly, there is no need to include LCD.h in the sketch.

Also keep in mind that the i2c controller that is on the backpacks supported by that library (as well as many others) is a PCF8574 and there is no "standard" way of hooking it up to the hd44780 LCD display.
As a result, the sketch must tell the library the i2c address as well as how the PCF8574 is wired up to the LCD.
If the i2c address or the pin mappings specified are incorrect it will not work.

As an alternative I'd suggest having a look my hd44780 library package which can be installed using the library manager.
It can auto self configure the i2c address as well as the pin mappings so the sketch does not have to specify this configuration information.
To use it instead of fm's library in your sketch, you will have to change the sketch to use different include files as well as change the lcd object declaration. But other than that, the rest of the sketch code should "just work".
You can read more about it here:

The main page as information about the h/w and s/w requirements, how to install it and a summary of all the API functions.
The wiki has some additional information about it and the hd44780_I2Cexp i/o class that you will need to use for a PCF8574 based backpack.

--- bill