Cold Cranking Amps.  This is a measure of the maximum output current that
can be obtained from the battery which is limited by the battery's internal
resistance.  In general, higher CCA is better, but the other measures of a
battery are the energy it stores (usually measured in amp-hours) and the
reserve time.  Many times a battery manufacturer will sacrifice one of these
at the expense of the other.  The actual CCA you require is dependent upon
the vehicle (4 cylinders are easier to turn over compared to 8 cylinders)
and the climate where the vehicle is driven (colder means heavier oil and
more power to turn the starter so draws more current).

Bob