A telemarketer is a person or business who tries to sell their services or products via the telephone. Unfortunately, criminals may try to call you under the guise of a telemarketer, with the hopes of getting your private information.
The US Government enacted a do-not-call list that helped decrease the number of calls that people get. but this hasn't stopped it altogether. Telemarketers may disregard this list and call or they may call if you signed up for a product or service where you allow the business to call you.