Can someone tell us the difference between generic drugs and original drugs?

Iressa, the original research drug, has a large investment in early research and development, so the clinical evaluation method must adopt rigorous phase III clinical research to prove its efficacy, while the generic drug only needs to do bioequivalence tests of healthy people to compare the drug properties of generic drugs and the original research drug, but bioequivalence does not mean clinical equivalence. In terms of therapeutic effect and safety, the original drug Iressa is more effective.