Answer:
open source Software
Explanation:
An open source software can be any software made available within an open source license which means that anyone can access its source code, see that it was created and, as the question says, "study, change and improve it."
This is contrary to copyrighted or closed source software where you would require a license to use the software, however, we can not see or amend in the "building blocks" (i.e. code)
