A system is a group of regularly interacting or interdependent items forming a coherent whole. It is defined by its Boundary, i.e. by what is and what is not part of it. System boundaries can be described as Markov Blankets.
Each item that is part of a system can itself be understood as a system. This means that described abstractly, The world is a hierarchy of systems.
A system can be fully characterised by describing the evolution of its states. This means that ontologically, Systems live in state spaces.
Systems emerge due to constraints.
If they change over time, we call them Dynamical Systems.
References
- Friston (2018): “A free energy principle for a particular physics”
- Merriam-Webster: “System”
- Ramstead et al. (2019): “Multiscale integration: beyond internalism and externalism”