A coincidence is a surprising concurrence of events, perceived as meaningfully related, with no apparent causal connection (Diaconis and Mosteller 1989).
See also Birthday Problem, Law of Truly Large Numbers, Odds, Probability, Random Number
References
Bogomolny, A. ``Coincidence.''
http://www.cut-the-knot.com/do_you_know/coincidence.html.
Falk, R. ``On Coincidences.'' Skeptical Inquirer 6, 18-31, 1981-82.
Falk, R. ``The Judgment of Coincidences: Mine Versus Yours.'' Amer. J. Psych. 102, 477-493, 1989.
Falk, R. and MacGregor, D. ``The Surprisingness of Coincidences.'' In Analysing and Aiding Decision Processes
(Ed. P. Humphreys, O. Svenson, and A. Vári). New York: Elsevier, pp. 489-502, 1984.
Diaconis, P. and Mosteller, F. ``Methods of Studying Coincidences.'' J. Amer. Statist. Assoc. 84, 853-861, 1989.
Jung, C. G. Synchronicity: An Acausal Connecting Principle. Princeton, NJ: Princeton University Press, 1973.
Kammerer, P. Das Gesetz der Serie: Eine Lehre von den Wiederholungen im Lebens--und im Weltgeschehen. Stuttgart, Germany:
Deutsche Verlags-Anstahlt, 1919.
Stewart, I. ``What a Coincidence!'' Sci. Amer. 278, 95-96, June 1998.