"Coppia" is a lot of things. It surely works for two people in love with each other, but also to a pair of something, mostly living things: you're less likely to hear "una coppia di viti" as it's most used the translation of pair "un paio di viti" to say "two bolts", for example. But you can hear it for example in poker or card games in general where it's used "coppia di re" as "pair of kings".
Another time when the word "coppia" is used is when referring, in physics, to torque, which can be translated both as "coppia" and "momento" (there is a difference, but it's the same as the english torque vs. momentum). For example when talking about engines the word coppia is the most used "la coppia erogata dal motore"="the torque delivered by the engine"
noctuatacita, in this case the torque power is called coppia motrice, because it's about the moment when the force of the combustion in the cylinder coming down vertically from the piston transforms into the rotating force of the crankshaft. So my understanding is that the torque is the power of the two working together. So the coupling of them. (I'm no engineer)