residuals is a generic function which extracts model residuals
  from objects returned by modeling functions.
The abbreviated form resid is an alias for residuals.
  It is intended to encourage users to access object components through
  an accessor function rather than by directly referencing an object
  slot.
All object classes which are returned by model fitting functions
  should provide a residuals method.  (Note that the method is
  for residuals and not resid.)
Methods can make use of naresid methods to compensate
  for the omission of missing values.  The default, nls and
  smooth.spline methods do.
residuals(object, …)
resid(object, …)an object for which the extraction of model residuals is meaningful.
other arguments.
Residuals extracted from the object object.
Chambers, J. M. and Hastie, T. J. (1992) Statistical Models in S. Wadsworth & Brooks/Cole.
coefficients, fitted.values,
  glm, lm.
influence.measures for standardized (rstandard)
  and studentized (rstudent) residuals.