QMK song player is a web app that reads QMK song code and plays it in your browser.
If you have a QMK keyboard with a speaker, you can use the audio feature to produce these songs from your keyboard (how to add songs to your keymap). Why do this? Because it is fun! You can play a song when the keyboard starts up, or more functionally, play a little melody to indicate events like when setting the default layer.
QMK comes with a good number of predefined songs out of the box. Here are a couple to whet your appetite:
More songs are in quantum/audio/song_list.h. You can also edit the code and write your own songs, see QMK song syntax for how to do it. Enjoy!
Thanks! Haha, yes, I see in hindsight how this looks like an acronym confusion.