A seventh chord in music theory is plainly a triad with the addition of the “7th interval” above the triad’s root. For example, the combination C, E, G, B is a seventh chord.
Scales in music theory are not just bounded by Major vs Minor distinctions. It turns out that all scales can be represented via modes. Modes are just another way of producing a certain tone/mood commonly associated with a happy (Major) or melancholic (Minor) sound.
Motivation Growing up, I always found it hard to memorize key signatures of keys I wasn’t familiar with. This especially held true for minor keys since I did not play much minor pieces as a starting Classical pianist.