A derivative is a contract between two parties whose value depends on something else — the underlying, such as a share, an index, a currency or a commodity. You don't own the underlying thing; you own a promise about it. Most derivatives also have an expiry: a date when the contract ends and is settled, whatever has happened by then.
That's why they behave so differently from a share. A share can be held for decades and gives you a claim on real profits. A derivative pays nothing along the way and is often built with borrowed exposure. Every contract also has someone on the other side, so one party's gain is the other's loss: derivatives move money between the two sides rather than creating it, costs come out of both, and many finish worthless at expiry.
You own the promise, not the thing. When the date arrives, the promise is all there is.
Educational content only. It is not personal financial advice.