What is difference between listed and unlisted company?

Sec 2(23A) "listed public companies" means a public company which has any of its securities listed in any recognized stock exchange.

You also can see Form of annual return of a company having a Share capital SCHEDULE V, PART II, from there you easily identify that whether the company is listed or not.

Each company (Indian or foreign) has a unique CIN (Corporate Identity Number).If the CIN starts with "U" then its Unlisted and if it starts with "L", its listed.