License
A license is the short legal text in a repository that says what other people may do with the code.
What it tells you about a developer
A developer who put licenses on their projects thought about other people using their code. A maintainer who chose a license deliberately has engaged with how software gets shared and sold, which matters on any team that builds on open source.
Publishing code makes it visible, and the license is what makes it usable. Permissive licenses like MIT and Apache let anyone use the code for anything, including selling products built on it. The GPL family requires that changes be shared back in the open. Public code with no license stays all rights reserved. Choosing a license is the moment open sourcing becomes a deliberate decision.