How do you define Team Culture?

There is no formal definition. That is the beauty that there is no formal definition of that a team culture is. Plainly put, team culture is what a team/individuals DO when not being watched

People and Process are part of the Culture. People with a certain mindset come together to define what their culture is. To enforce and sale they come up with process. People and Process alone is not culture. Often we get too carried away in process (or people for that matter) that we forget why this was there and what was the purpose of that process.

Is culture fixed, or does it change over time?

Culture always has to evolve and stay relevant with the purpose. Team’s evolution is well described with Tuckman’s stages - Forming, Storming, Norming, Performing. This can even be seen as a cycle. The culture also has to reflect the stage.

What is more important? Culture or Strategy?

Both. Quoting the popular saying from Peter Drucker “Culture eats strategy for breakfast”. A Team culture has a stronger influence on success than any strategy or plan. Even the best strategy will fail if the people, values, behaviors, and everyday habits within the organization don’t support it. I will go little further and say strategy like said is the Breakfast, it gives the team the direction. Quoting another famous line “Hope is not a strategy”