  Anelasticity, as an intrinsic property of amorphous solids, plays a
significant role in understanding their relaxation and deformation mechanism.
However, due to the lack of long-range order in amorphous solids, the
structural origin of anelasticity and its distinction from plasticity remain
elusive. In this work, we study the transition from anelasticity to plasticity
transition in a two-dimensional model glass. Three distinct mechanical
behaviours, namely elasticity, anelasticity, and plasticity, are identified
with control parameters in the amorphous solid. Through the study of finite
size effects on these mechanical behaviors, it is revealed that anelasticity
can be distinguished from plasticity. Anelasticity serves as an intrinsic
bridge connecting the elasticity and plasticity of amorphous solids.
Additionally, it is observed that anelastic events are localized, while plastic
events are subextensive. The transition from anelasticity to plasticity is
found to resemble the entanglement of long-range interactions between element
excitations. This study sheds light on the fundamental nature of anelasticity
as a key property of element excitations in amorphous solids.
