The term dark matter might sound corny and from science fiction but its effects can be observed.

For example, American astronomers in the 70’s observed that speed of rotation at the edge of spiral galaxies is the same as speed of rotation close to center of the galaxy. This should not be possible because the gravity reduces as distance from center increases. But this can be explained through the existence of mass we cannot see that engulfs spiral galaxies with a diameter significantly larger than the galaxy.

Swiss Astronomer Zwicki first observed effects of unseen matter in his experiments and called the unseen mass dunkle Materie ('dark matter'). The guy who discovered it gets dibs on naming. That how its always been.