Okay kiddo, so you know how in music we have different sounds and notes? Well, sometimes we put some of those notes together to make really cool sounds. One of those cool sounds is called a "nondominant seventh chord."
Now, a chord is when we play three or more notes at the same time. And a "nondominant" chord means it's not the most important one in the song.
So, a nondominant seventh chord is when we play four notes at the same time, and they make a special sound. These four notes are usually the first, third, fifth, and seventh notes in a scale.
When we put these notes together in a nondominant seventh chord, it creates a unique feeling in the music. It can sound happy or sad, depending on how we use it.
Overall, a nondominant seventh chord is just a fancy way of saying a group of four specific notes that make music sound really cool and interesting.