What is Copyleft? 🤔🤔

a) A method for making a piece of software free of charge, and all modified versions free of charge.
b) A method for making a piece of software #FreeSoftware, and all modified versions Free Software.
c) A method to enable a piece of software to be copied.
d) Another term for copyright used when talking about software.

#SoftwareFreedom #Licensing