Don’t ask us – we don’t know what it means either.  But at http://yeroon.net/ggplot2/ you’ll find a wonderful graphical interface to Hadley Wickham’s ggplot2 package.  With ggplot you can very easily produce some very sophisticated plots, but there is a lot to learn and the Yeroon site can help you get started.

To give it a try, paste the following into R to produce a data set to work with,

quakes$depth.class <- cut(quakes$depth,4) 
levels(quakes$depth.class) <- c("A","B","C","D") 
write.csv(quakes,"quakes.csv",quote=F,row.names=F) 

This produces the file quakes.csv in your working directory.  Next, navigate to Yeroon and

1. From the Open Data menu, select Upload File, and import the quakes.csv file we just created.
2. In the centre panel,
1. Right click, select Map x and choose long
2. Right click select Map y and choose lat
3. Right click, select Facet then Map and choose depth.class
4. Right click, select Add Layer then Bivariate Geoms and choose points
3. In the Layers panel on the left, right click on points, select color then Map and choose mag
4. From the View menu, tick code panel
5. Finally, click the Draw Plot button below the centre panel

In the code panel at the bottom Yeroon gives you the code needed to produce the plot in R

library(ggplot2) 
myData <- read.csv("C:\fakepath\quakes.csv", header=T, sep=",", dec=".") 
ggplot(myData, aes(x=long, y=lat)) + geom_point(aes(colour=mag)) + 
  facet_wrap(~depth.class)

and in the centre panel Yeroon shows the result

Quakes plot produced by Yeroon