Noun
the set of functions F(x) + C, where C is any real number, such that F(x) is the integral of f(x)
Source: WordNetThe indefinite integral, or antiderivative, is written: : Functions differing by only a constant have the same derivative, and it can be shown that the antiderivative of a given function is actually a family of functions differing only by a constant. Source: Internet
Some authors define the indefinite integral of a function as the set of its infinitely many possible antiderivatives. Source: Internet
When the word integral is used without additional specification, the reader is supposed to deduce from the context whether it is referred to a definite or indefinite integral. Source: Internet