Let's first understand the need to have different names for medicines. To put this theory in simple words, orange juice is something consumed everyday, but an orange juice manufacturing company would want to give their product a unique name that is different from the common tag "orange juice" and this new name becomes its brand name. Similarly, a generic name is a chemical name given to a medicine keeping in mind the active ingredients present in it. A brand name is a name given by the manufacturing company to differentiate their product from other similar products in the market. Another important reason behind giving brand name to a medicine is that generic names are long and can be difficult to remember, while a brand name will always be short and easy to remember.
Generic medicine is defined as a substitute or a bioequivalent of a branded medicine with respect to pharmacokinetic and pharmacodynamic properties. A medicine can only be termed as generic if it is made up of the same chemical composition at same strength and it has to meet the same pharmacopoeial standard of preparation. Generic medicines are consumed in similar dosage pattern, strength, safety precautions as its innovator brand.
Many large pharmaceutical companies are heading towards manufacturing their own generic medicine to preempt the expiry of their patent. Patent lifetime differs from country to country and also it differs for different medicines. Generally, there is no such process where you can renew a patent once it has expired.
In the United States the FDA carries the responsibility to make sure that generic drugs are safe and effective. This process began in 1960s where generic manufacturers had to prove their medicine is bioequivalent to the innovator brand. The parameters for approval of generic medicine are same as its innovator brand. Generic medicines are cheaper and can save patients and insurance companies thousands of dollars without compromising the quality of care.