Okay kiddo, so you know how when you listen to music it sounds like it goes up and down and sometimes makes you feel different emotions? Well, there is a special pattern of chords in music that can make you feel a certain way too.
The bvii-v7 cadence is a fancy name for a pattern of two chords that often shows up at the end of a song or section of music. The first chord in the pattern is called "B flat major" but we'll just call it the "B flat" chord. This chord sounds kinda sad or serious. The second chord is called "A flat dominant 7" but we'll just call it the "A flat 7" chord. This chord sounds like it kinda wants to go somewhere else, like it's excited and wants to move forward.
When we put these two chords together in a pattern, it makes us feel like the music is almost over, but not quite. Like we are waiting for something to happen. This can create a feeling of tension or anticipation in the music that makes us want to keep listening to see what happens next.
So, to summarize: the bvii-v7 cadence is a special pattern of two chords in music that can make you feel like something is about to happen, kind of like when you are waiting for a surprise and you feel excited and curious.