Noun

1. the number of neutrons or protons in nuclei which are required to fill the major quantum shells, and thus produce exceptionally stable nuclei - 2, 8, 20, 28, 50, 82 & 126
2. A metric used to determine a team's required performance to make the playoffs.
   1. The sum of one and the wins by one team and losses by an opponent necessary for the team to ensure the opponent cannot catch it in the standings by the end of the regular season. In Major League Baseball, with a regular season of 162 games, the magic number M is calculated as M = 163 - W₁ - L₂, in which W₁ is the leading team's current win total, and L₂ is the opponent's current loss total. A magic number of 0 indicates that the trailing team cannot catch the leading team.
   2. By extension, the lowest such number that assures a team a playoff berth.
3. 1. a number which is manually entered in a sourcecode repeatedly, rather than defined somewhere as a named constant. Especially one which is arbitrary or lacks explanation.
   2. a number which cannot occur in normal use, used as a placeholder (e.g. a fictitious date such as 2000-02-32) or for other purposes (e.g. where the string slicing function RIGHT or RIGHT$ is not implemented, the same effect can be achieved by using (e.g.) MID(A,3,10538) or MID(A,3,6031769) to achieve the effect of RIGHT(A,3), because no feasible string is anywhere near that long).
   3. a hash code, such as those used by some webmail servers to keep track of sessions.