Who is CAS? http://www.computingatschool.org.uk/
Its is a organisation who's job is to develop support and training for teaching Computing and in particular the computer science aspects of the new curriculum. They where one of the organisations who worked on the proposed curriculum and have been recently funded by the DfE.
What is a Master Teacher? - Me, I'm one :o)
A teacher who has skills and expertise in the area of Computing and who wants to share this with others though running CPD session. Normally they will be involved in hub meeting but also they will run more specific training for teachers. http://community.computingatschool.org.uk/events
What is a CAS hub?
Its is a community of teachers who come together to develop and share ideas for the teaching of computing. Its about helping and supporting one another. Different hubs can work in different ways but the important thing is that after a session you should leave excited and with a new idea to use back in school.
Details for the Hammersmith CAS hub which I am running is below.