Leak firmware

I want to know, what is a leak and who creates the leaked firmware ?
It's coming from Meizu ? or just a group of people which try to improve the firmware ?

Thanks

a leak is a test-firmware released by jack wong or a meizu developer...just for testing-purposes!
some fans modify firmwares as well but you couldn´t call that ones leak because there is nothing improved...just changed designs or translations or whatever!

ah, i think the last customized russian firmware was quite advanced.
I would not call firmwares from other sources 'leaks' but 'custom firmware'

Official Firmware = Firmware that is stable enough to sell a product with.
Leaked Firmware = Firmware compiled for testing purposes and released to get feedback or without consent of the programmer by one of the testers.
Custom Firmware = firmware from other sources for what purpose and improvements ever.

ok, thank you for your answer !