I have a phenomenon in mind but can't remember the name. Without name or other keywords, I can google for the rest of my life. Where, in general, should I ask in such a case?
The concrete thing I can't remember the name of right now is the relativistic effect that alters classical gravitational orbits to lose energy so the orbiting objects will finally collide. (Each object "sees" the other at some point slightly behind the position where it would be in the classical case, so gravitational pull is not exactly perpendicular to the orbit.)