The Apache License is a permissive open-source software license that allows users to freely use, modify, and distribute software. It was created by the Apache Software Foundation to promote collaboration and innovation while ensuring that contributors receive credit for their work. The license also includes a grant of patent rights from contributors to users, which helps protect against patent litigation. One of the key features of the Apache License is that it does not require derivative works to be open-sourced, allowing developers to create proprietary software based on the original code. This flexibility has made it popular among many projects, including those in the Apache ecosystem, such as Apache HTTP Server and Apache Hadoop.