A category modeled after the properties of the category of sets. A category 
is a topos if 
has finite limits and every object of 
has a power object (Barr and Wells 1985, p. 75)
Topos
See also
Category, LogosExplore with Wolfram|Alpha
References
Barr, M. and Wells, C. Toposes, Triples and Theories. New York: Springer-Verlag, 1985.Freyd, P. J. and Scedrov, A. Categories, Allegories. Amsterdam, Netherlands: North-Holland, 1990.MacLane, S. and Moerdijk, I. Sheaves in Geometry and Logic: A First Introduction to Topos Theory. New York: Springer, pp. 24-30, 1994.McLarty, C. Elementary Categories, Elementary Toposes. New York: Oxford University Press, 1992.Referenced on Wolfram|Alpha
ToposCite this as:
Weisstein, Eric W. "Topos." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Topos.html