1. Law - security.
In the law of security and charges over assets, crystallisation is the transformation of a floating charge over assets into a fixed charge.
Crystallisation happens on the appointment of an administrative receiver, on the presentation of a winding-up petition, or as otherwise provided for in the document creating the charge.
2. Tax and financial reporting.
In tax and financial reporting, crystallisation is the change of an unrealised gain or loss to a realised one.