Beginner: The audience has beginner experience on Ubuntu and Linux, and might not have deep understanding of open source communities. Think about sessions that will allow someone getting started to jump to the intermediate level
Intermediate: This audience has many experiences using Ubuntu and Linux, and might already be participating in open source communities. We can also suppose that they use CLI and other tools included on Ubuntu for their needs. Sharing knowledge or experiences on specific area, know-hows on troubleshooting would be suitable.
Advanced: These audiences already have a deep understanding of Ubuntu, its ecosystems and related open source technologies, and actively use Ubuntu on their projects and work. They might also actively participate and contribute to open source communities. Topics on internal implementation, how the internal system works and its application would be suitable.