https://www.musical-u.com/learn/how-to-learn-intervals/
All great musicians rely on their sense of what’s called “relative pitch” to play and understand music. “Relative pitch” is the ability to accurately hear the distances between notes. The core skill of relative pitch is therefore “interval recognition“: being able to tell exactly how far apart a pair of notes are. https://www.musical-u.com/learn/how-to-learn-intervals/