Plasticity in mechanics means irreversible deformation, the opposite of elasticity

Evidence

In mechanics, a material is called plastic if it cannot return to its initial form after undergoing a deformation. ”Plastic” in this sense is opposed to ”elastic.” Plastic material retains an imprint and thereby resists endless polymorphism. This is the case, for instance, with sculpted marble. Once the statue is finished, there is no possible return to the indeterminacy of the starting point. So plasticity designates solidity as much as suppleness, designates the definitive character of the imprint, of configuration, or of modification. — Catherine Malabou, What Should We Do with Our Brain?, 62

Categorization

• DEFINE: The core technical meaning that anchors the whole plasticity-vs-flexibility distinction.
• ADDENDUM: Directly useful for distinguishing plasticity (gives/receives form, resists infinite reshaping) from flexibility (only receives) — the reader’s core goal.
• XREF: connects to: Plasticity means receiving form while resisting deformation, and extends to tissue regrowth — Catherine Malabou, The Future of Hegel: Plasticity,…, 226; Plasticity is suppleness that is neither passion nor passivity — Catherine Malabou, The Future of Hegel: Plasticity,…, 290