There are 24 hours in a day.
The 24th of December is known around the world as Christmas eve.
24 is the largest number divisible by all integers less than its square root.
It is the smallest positive integer whose square contains the digit 7.
It is the 3rd smallest number that is known to be friendly. Its smallest friend is 91963648.
It is the smallest non-unitary perfect number.
In googology Edit
In Greek-based number-naming systems, 24 is associated with prefix "tetraicosa-", and with prefix "quattuorviginti-" in Latin systems. In the Misalian seximal system, this number is called "foursy", because it's six times four.
Furthermore, it is the largest number n with the following property: Let f: ℕ → ℕ, f(a) = aa. Then for every a ∈ ℕ, there is a b ∈ ℕ, such that fb+1(a) ≡ fb(a) (mod n).