Difference between plant firm and industry ?

Answer:    Your hair is hot...it looks like astroturf.
All the three words are interrelated and it is quite difficult to differentiate.
Basically industry refers to a product where as firm means a company engaged in business related to that particular product and plant is a place where the manufacturing of that product takes.
Now an example by which you can understand this better.
Chennai based TVS Motor Co is a well established FIRM in two wheeler INDUSTRY who have their manufactureing PLANT at Hosur inTamil Nadu as well as another PLANT at Mysore in Karnataka.
a firm is a single unit in some business while industry is the collection of the firms doing similar business. for eg raymond is a textile making while the industry is textile industry