What does it mean to be modular?

Oliver gave a talk in the seminar series on behavior trees in robotics entitled What does it mean to be modular?

For more details you can check out this publication:

On modularity in reactive control architectures, with an application to formal verification
O Biggar, M Zamani, I Shames
ACM Transactions on Cyber-Physical Systems (TCPS) 6 (2), 1-36