closed set
set whose complement is an open set
empty set
mathematical set containing no elements
clopen set
subset that is both open and closed
shift space
set of infinite words that is closed with respect to the natural product topology and invariant under the shift operator
closed interval
(possibly infinite) interval that includes all of its limit points
Julia set
fractal set named after Gaston Maurice Julia
perfect set
subset of a topological space that is closed and has no isolated points
boundary
dividing line between two areas or sets of points in a topological space; difference between the closure and the interior
club set
closed cofinal subset of an ordinal
closed ball
mathematical ball that includes its bounding sphere