A high-pass filter is like a special helper for your ears that helps you hear certain sounds more clearly. You know how some sounds are really low and rumbly, like when a truck goes by, and other sounds are higher and squeakier, like when a bird chirps? A high-pass filter helps you hear the higher squeaky sounds better by taking away some of the low rumbly sounds.
It's kind of like putting a strainer over a pot when you're cooking spaghetti. The strainer lets the water drain out but keeps the noodles in the pot. A high-pass filter lets the high-pitched sounds go through but stops the low-pitched sounds from getting to your ears.
So, if you have some music playing and you turn on the high-pass filter, you might notice that the bass (the really low rumbly sound) seems quieter, but you can hear the higher notes and instruments more clearly. It's like putting a spotlight on the sounds that are higher up in the music.