means The act of getting in the way of something — whether a process, a signal, or another person's plans — or, in physics, the way overlapping waves combine to reinforce or cancel each other.

from From Latin 'inter-' (between) plus 'ferire' (to strike), via the verb 'interfere' — literally to strike or come between. The same 'ferire' (to hit, to wound) lurks behind words for striking blows, so 'interference' carries the old sense of two things colliding mid-air. The wave-physics meaning was borrowed into English in the early 19th century when scientists needed a word for light and sound waves crashing into one another.