What is a Chinese Lucky Coin?

Excuse me, could you elaborate on what exactly a Chinese Lucky Coin is? I've heard of them being used as symbols of prosperity and good fortune, but I'm not entirely sure of their origin or cultural significance. Are they typically made of a specific material? Do they have any inscriptions or symbols on them? And how are they commonly used or given as gifts? I'd love to learn more about this fascinating aspect of Chinese culture.