What is a derivative in trading?

Could you please explain what a derivative is in the context of trading? I've heard this term mentioned frequently but am still a bit unclear on its exact meaning. Could you elaborate on its characteristics and functions in the trading world? Also, could you provide some examples of common types of derivatives that are traded? I'm particularly interested in understanding how they are used to hedge risks and speculate on market movements. Thank you for your assistance in clarifying this concept for me.