Current directions in ostracism, social exclusion, and rejection research, 2019: pp. 1-2 (social exclusion is a broad category encapsulating various types of negative interpersonal experiences in which someone feels kept apart from others physically, emotionally, or otherwise devalued socially; exclusion experiences may involve someone receiving direct negative attention (rejection-based exclusion) or being ignored in some way (ostracism-based exclusion) p. 3 (Rejection researchers typically define the construct as a direct communication that one is not wanted; the conceptual definition of rejection can be extended to involve discriminatory behaviors that make someone feel that they are unwanted, either interpersonally or at the societal level; subtle forms of rejection experience on a daily basis, called microaggressions)

APA dictionary of psychology, 2015 (rejection 1. denial of love, attention, interest, or approval. 2. an antagonistic or discriminatory attitude toward a group of people)

Annual review of psychology, 2007: p. 427 (Ostracism: ignoring and excluding individuals or groups by individuals or groups; Rejection: an explicit declaration that an individual or group is not wanted; Social exclusion: being kept apart from others) p. 429 (Ostracism is typically defined as being ignored and excluded, and it often occurs without excessive explanation or explicit negative attention. Ostracism is often operationalized as a process that is characterized as an unfolding sequence of responses endured while being ignored and excluded; Social exclusion appears to be defined as being excluded, alone, or isolated, sometimes with explicit declarations of dislike, but other times not; Rejection is typically operationalized as a declaration by an individual or group that they do not (or no longer) want to interact or be in the company of the individual)

Here are entered works on the explicit declaration that an individual or group is ignored or excluded. Works on ignoring or excluding an individual or group, often without an explicit explanation or declaration, are entered under Ostracism (Psychology).