Eligible assessee for the purpose of Section 44AD means an individual, HUF or a partnership firm, who is a resident, but not an LLP.
Turnover from eligible business should not exceed 2 crore rupees (wef AY 17-18). Eligible business here means any business except the business of plying, hiring or leasing goods carriages (Sec 44AE).
The provisions of Section 44AD shall not apply to:
a) a person carrying on profession u/s 44AA
(b) a person earning income in the nature of commission or brokerage; or
(c) a person carrying on any agency business.
So in simple terms, any person who fulfis the above conditions can opt for Section 44AD.