Assuming You're using the same LCD library I'm using, there is a longer form of the constructor that takes pin assignments for the different pins on the I2C module, as Majenko says.
I'm at work, so I don't have access to my code, but your constructor looks a whole lot like the one I use for my module, which has non-standard pin assignment. (I got my LCD modules from oddWires, and they came without documentation. I had to do quite a bit of detective work to figure out how to make them work.)
I use the Newliquidcrystal_1.3.5 library in my project, to interface the above-mentioned oddWires I2C LCD display. That library has various constructors, one of which takes all the parameters you list. Those extra numbers indicate the pins that connect to the I2C module.
My oddWires LCDs need exactly the settings you list in the constructor. Your milage may vary.
The long form is defined in the library header with
From the naming of the parameters you can deduce most of them:
- En is an enable line
- Rw is a read/write line?
- Rs is ?
- d4-47 are the data pins
- backlightPin is the pin that turns backlight on and off
- pol indicates the backlight polarity (
POSITIVE probably means pull the line high to enable the backlight.