Other forms: interplays
Interplay is a kind of back-and-forth interaction in which each side affects the other. A beautiful piece of music has the perfect interplay between melody, rhythm, and harmony.
You can think of interplay as if you're watching an actual play on a stage: the way two characters communicate, whether they're cooperating or clashing with each other, is a kind of interplay. This word is often used in a less concrete way, so you might hear a sociologist talk about the interplay between race and class or a film critic discuss the interplay between violence and comedy in a movie.