Immanuel Kant's theory of morality, the categorical imperative, states that it is immoral to use another person merely as a means to an end, and that people must, under all circumstances, be treated as ends in themselves.

This is in contrast to some interpretations of the utilitarian view, which allow for use of individuals as means to benefit the many.

 Idiom

A means to an end is also an idiom.

 It often refers to an activity (such as an undesirable job) that is not as important as the goal you hope to achieve (monetary gains for example).

For example, Mike doesn't have any professional ambitions.

 For him, work is just a means to an end.

One starts something and finishes it, without that something leading into something else.

Thus, it is an end in itself