When do we consider a given substance as waste?

Waste is something unwanted or unusable material. It is any material which is no longer useful as it has served its purpose or at the end of the process has no further use and it is generally discarded. For example, Garbage that we daily produce in our home. Food that we eat goes into our body. It is then acted upon by various specific enzymes which are needed for the breakdown of these large food molecules into simpler small molecules which provide energy. Materials like plastic which cannot be broken down by bacteria’s or enzymes are non-biodegradable (cause threat to human health). Hence these products are also called waste. For example polythene bags, metal scarps.