Combobreak is a term used to describe a player losing their combo during any part of a beatmap. By default, they will play a "combobreak sound" if the player has broken a combo of 21x or higher. And if enabled in the settings, a combo burst image will appear at certain milestones.
There is no in-game option to disable the combobreak sound effect. Players who do not want to hear the combobreak sound may replace the combobreak.wav file with a blank or silenced .wav audio file.