Can someone explain hyperfocus?

So on this forum I have heard the term, "hyperfocus" regarding how romantic adhd partners can be at the start of a relationship. Does this mean that their romantic acts are not fueled by actual love but by there Adhd? Or are they in love when they are romantic but their adhd just makes them show it more? What makes this different than your typical relationship "honeymoon" stage and "comfortable" stage. Every relationship has a honeymoon stage at first and then people get comfortable. How is hyperfocus different than that and how different is it from other relationships when it goes away?