Contextual explanation: Sudden, rapid loss of stability in a system. 
Abrupt destabilisation is best understood as a process—specifically, a rapid and fundamental transformation in which a system quickly loses its previous stability and shifts into a new, often less desirable, state. This can occur in physical, social, ecological, or technological systems, and is marked by the speed and severity of the change.

Themes: Instability and systemic change. 
Abrupt destabilisation is closely tied to the theme of systemic change, highlighting how systems can undergo dramatic shifts rather than gradual evolution. It also relates to instability, as the process disrupts established patterns and can lead to unpredictable outcomes.

Nuance: Rapid, non-linear transition.
What distinguishes abrupt destabilisation within its category is the speed and non-linearity of the transition. Unlike gradual decline or steady transformation, abrupt destabilisation involves a tipping point or trigger that causes a swift and often irreversible change, making it critical to understand for risk assessment and resilience planning.