Of course, the overarching theme of the Jam is services - but there will be a special Secret Theme for the weekend too. This Secret Theme will carefully chosen by representatives of the worldwide organising team, and kept Top Secret until it is announced on the Friday evening (local time) in each location.
We expect the Theme will be quite abstract, to allow a wide range of practical applications, depending on the participants' interests.
Here's an example from the last Global Service Jam. Last year, it had the theme: "(Super)HEROES". The participants interpreted it in many different ways, producing many different types of services based on sharing, helping, empowerment, or even super-powers.
The Theme of the last Global Sustainability Jam (our sister event) was "PLAYGROUNDS", so participants developed lots of projects about play, education, the use of spaces, and encouraging play in other contexts.
The Global Service Jam is more about tools, methods, people, ideas and exchange than any particular field of application.