A blacklist (or black list) is a list or register of entities or people, for one reason or another, are being denied a particular privilege, service, mobility, access or recognition. As a verb, to blacklist can mean to deny someone work in a particular field, or to ostracize a person from a certain social circle.

Conversely, a whitelist is a list or compilation identifying entities that are accepted, recognized, or privileged.

The term blacklisting may be used in a pejorative sense, implying that a person has been prevented from having legitimate access to something due to inappropriate covert actions of those who control access. For example, a person being served with a restraining order for having threatened another person would not be considered a case of blacklisting. However, somebody who is fired for exposing poor working conditions in a particular company, and is subsequently systematically blocked from finding work in that industry, is described as having been inappropriately and often illegally blacklisted. Blacklisting can and has been accomplished informally by consensus of authority figures, and does not necessarily require a physical list or overt written record.

Blacklisting can be formal or informal. In the employment setting, applicants who apply to numerous positions regardless of being qualified or not can soon be ignored during some or all subsequent applicant processes. This can be an informal choice made by one person or a shared formal response taken up by one office, and not an issue that would be described as blacklisting. In the past, blacklists of union members have been shared or circulated between multiple organizations to prevent hiring of employees who, rather than being incompetent, have been critical of management actions. People have been prevented from working for decades due to being on a blacklist; in some cases the information on the blacklist was false.[1]