The document explains the GNU General Public License (GPL), which is a widely used free software license that guarantees end users the freedom to run, study, modify, and distribute software. It emphasizes the 'copyleft' concept, requiring that derivative works also remain free and be licensed under the same GPL terms, while also addressing common misunderstandings and stipulations regarding commercial use of GPL software. The document provides practical examples, FAQs, and discusses the implications of GPL licensing, especially in relation to popular projects like WordPress.