scientifically correct annotation for residuals of a model

Hello,

Maybe that is a little bit offtopic, but pls have a look e.g at this plot:
http://itl.nist.gov/div898/handbook/pmd/section4/plots/mvpt6_f.gif

where the residuals of a model are plotted against another variable.
Now I want to know if there is a scientifically correct term/string
to describe the residuals of a model (e.g Y~log(x1)+(x2)) ...
I am thinking e.g. about:

expression(epsilon[Y~log(x1)+(x2)])

What is the correct term and how to write in R as expression?

/Johannes


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