Infinity is an unbounded quantity greater than every real (and every whole) number.

aleph | aleph-0 | aleph-1 | cardinal number | complex infinity | continuum | continuum hypothesis | countable set | countably infinite | directed infinity | division by zero | Hilbert hotel | infinite | infinite set | infinitesimal | l'Hospital's rule | limit | line at infinity | point at infinity | transfinite number | uncountably infinite | zero

high school level (California mathematical analysis standard)