User blog comment:BlauesWasser/Why Zero Shouldn't be considered a cardinal/@comment-11227630-20180501052236/@comment-30754445-20180501091349

All true.

Alternatively, a cardinal can be defined as an ordinal that has no bijections to ordinals that are less then itself. Since there are no ordinals less than zero at all, the ordinal 0 fits this definition of a cardinal as well.

0 is a very special cardinal, though. Aside from the obvious (it's the smallest one), there's a unique set with cardinality 0 (the empty set). For every other cardinal A, there's an infinitude of sets with A members.