There’s an article at Groklaw by the General Counsel of Red Hat Inc. about what exactly open source software is, the groundings of open source in copyright law, and how those rights are managed by open source licenses to enact the different goals embodied in different types of open source projects. It lays down the different types of licenses, and goes into detail about the GPL. It also lists some of the common myths about open source and why they’re really just myths, and lays down some best practices for companies working with or on open source. Certainly worth a read.