Tally marks scratched into a wolf's leg bone — found in what is now the Czech Republic, dated to roughly 30,000 BCE — record what is probably the oldest mathematical activity humans engaged in. Each notch matches one occurrence of something, in a one-to-one correspondence between marks and things being counted. Counting is the first mathematical technology, and in many ways it is the mathematical move: a recognition that quantity is a property of the world that can be tracked symbolically, separate from the things being quantified. Five sheep and five fingers share a property — five-ness — that exists independently of either, and is what mathematics from Euclid onward has set out to formalize.
Counting is, formally, a bijection between a finite set and an initial segment of the natural numbers {1, 2, …, n}. The achievement is conceptual: realizing that cardinality — the size of a collection — is an abstract property invariant under reordering, renaming, or replacing the things counted with anything else of the same number. Different cultures invented different number systems to support counting at scale: unary (tally marks, slow but immediate); base-10 (probably from finger-counting; standardized through Indian-Arabic numerals); base-20 (Mesoamerican, probably from finger-and-toe counting); base-60 (Babylonian, the source of our 60-second minutes and 360-degree circles); base-2 (binary, native to electronic computation). Place-value notation — the move that makes 23 differ from 32 — was a separate invention, not present in Roman numerals (where IXC means "a hundred minus ten plus one"... or does it?). The successor function — the operation of moving to the next number — is what Peano formalized into an axiom. The cardinal/ordinal distinction is subtle: cardinals describe how many (three apples), ordinals describe position in a sequence (the third apple), and they begin to differ for infinite collections — every countable infinite cardinal is the same (ℵ₀), but the ordinals stretch much further (ω, ω + 1, ω · 2, ω², …).
Counting underlies every dataset, every census, every measurement, every statistical analysis — data is just counts, in the end. Computers count in binary internally; the arithmetic logic unit of every CPU is, at root, a fast counter. Combinatorics, the branch of mathematics most directly descended from counting, is the basis of cryptographic key spaces, algorithmic complexity bounds, and most of probability theory. The little tally mark on the wolf's leg bone is the ancestor of every spreadsheet cell, every database row, every event-counted-by-a-script anywhere in the modern world.