Which term reflects a setback in progress or development?

The term that reflects a setback in progress or development is regression. This concept is often used to describe a situation where an individual, group, or system moves backward in terms of progress or development, indicating a decline from a previous state of advancement.

In various contexts, regression can occur due to various factors, such as reduced effort, loss of resources, or adverse conditions that hinder further development. This stands in contrast to terms like progress or advancement, which suggest moving forward or improving, and stagnation, which indicates a lack of progress rather than a move backward. Therefore, regression accurately captures the idea of reverting to a less developed state.