Complex is the head used for complex numbers.

ComposeSeries[series_1, series_2, ...] composes several power series.

Composition[f_1, f_2, f_3, ...] represents a composition of the functions f_1, f_2, f_3, ....

Conditioned[expr, cond] or expr \[Conditioned] cond represents expr conditioned by the predicate cond.

Conjunction[expr, {a_1, a_2, ...}] gives the conjunction of expr over all choices of the Boolean variables a_i.

ConnectedComponents[g] gives the connected components of the graph g.ConnectedComponents[g, {v_1, v_2, ...}] gives the connected components that include at least one of the ...

ConnectedGraphQ[g] yields True if the graph g is connected, and False otherwise.

Constant is an attribute that indicates zero derivative of a symbol with respect to all parameters.

ContourShading is an option for contour plots that specifies how the regions between contour lines should be shaded.

ContourStyle is an option for contour plots that specifies the style in which contour lines or surfaces should be drawn.