Meaning

noun the highest level or degree attainable; the highest stage of development

noun the extreme top or summit

adjective of the highest quality

originFrom the name of a brand of freeze pops originally made by a now defunct West Bromwich company called Crystallized Confections. The term is mainly used in the West Midlands and Wales but is sometimes used elsewhere in Britain and in Ireland.

Etymology from Wiktionary, CC BY-SA 3.0