  The physically relevant singularities occurring in FRW cosmologies had
traditionally been thought to be limited to the "big bang", and possibly a "big
crunch". However, over the last few years, the zoo of cosmological
singularities considered in the literature has become considerably more
extensive, with "big rips" and "sudden singularities" added to the mix, as well
as renewed interest in non-singular cosmological events such as "bounces" and
"turnarounds".
  In this article we present a complete catalogue of such cosmological
milestones, both at the kinematical and dynamical level. First, using
generalized power series, purely kinematical definitions of these cosmological
events are provided in terms of the behaviour of the scale factor a(t). The
notion of a "scale-factor singularity'" is defined, and its relation to
curvature singularities (polynomial and differential) is explored. Second,
dynamical information is extracted by using the Friedmann equations (without
assuming even the existence of any equation of state) to place constraints on
whether or not the classical energy conditions are satisfied at the
cosmological milestones. We use these considerations to derive necessary and
sufficient conditions for the existence of cosmological milestones such as
bangs, bounces, crunches, rips, sudden singularities, and extremality events.
Since the classification is extremely general, the corresponding results are to
a high degree model-independent: In particular, we provide a complete
characterization of the class of bangs, crunches, and sudden singularities for
which the dominant energy condition is satisfied.
