  We develop a suitable generalization of Almgren's theory of varifolds in a
lorentzian setting, focusing on area, first variation, rectifiability,
compactness and closure issues. Motivated by the asymptotic behaviour of the
scaled hyperbolic Ginzburg-Landau equations, and by the presence of
singularities in lorentzian minimal surfaces, we introduce, within the varifold
class, various notions of generalized minimal timelike submanifolds of
arbitrary codimension in flat Minkowski spacetime, which are global in
character and admit conserved quantities, such as relativistic energy and
momentum. In particular, we show that stationary lorentzian 2-varifolds
properly include the class of classical relativistic and subrelativistic
strings. We also discuss several examples.
