Yes this is a common mistake that most of people do while talking about the real estate industry.
Here is a simple answer:
Real estate agent: Also known as real estate associate, a real estate agent is a professional who has passed all the required exams along with the state level real estate licensing exam. He/she must be working under a broker.
Real estate broker: A broker comes on the higher level as compared to that of an agent in the real estate professionals’ hierarchy. He has completed the advanced education and has gone through additional training, which let him get the detailed knowledge of the real estate law.
Realtor: He/She needs to get the membership of National Association of Realtors (NAR) or Canadian Real Estate Association (CREA) and needs to maintain the standard and subscribe to the code of ethics for becoming a member of NAR or CREA. Every realtor is a agent, but every agent is not a realtor.