There is a sense in which the even integers can be considered "half" of all the integers: https://en.m.wikipedia.org/wiki/Natural_density https://en.m.wikipedia

There is a sense in which the even integers can be considered "half" of all the integers: https://en.m.wikipedia.org/wiki/Natural_density https://en.m.wikipedia.org/wiki/Natural_density "Counting stuff" can be generalised to infinite sets in different ways: cardinality is one (arguably the most common) of them, but natural density or measure are others.