public domain dedicates work to the public, waiving copyright so anyone can use, modify, or incorporate it into proprietary software without sharing changes back—maximizing adoption and simplicity. gpl, as used in the linux kernel, adds copyleft to require derivatives remain open source, ensuring collaborative freedom but restricting closed-source uses. you'd pick pd over gpl if your goal is broad reuse without enforcement, unlike linux's focus on perpetual openness.
gnu project
https://www.gnu.org/licenses/gpl-faq.en.html
linux kernel docs
https://docs.kernel.org/process/license-rules.html
