Definition
An anaphor is a noun phrase (NP) that obligatory gets its meaning from another NP in a given sentence. (Carnie, 2006, p. 145) Additionally, an anaphor must agree in gender, and often number, with its necessary antecedent.
Anaphors may also be susceptible to binding conditions and have restrictions on where they can appear in a sentence.
In English, words like myself, himself, herself, themselves, ourselves, etc., are typically described as anaphors while languages such as Halkomelem do not have these independent reflexive or reciprocal pronouns. (Gerdts & Hukari, 2000, p. 10)
Examples

References
Carnie, A. (2006). Syntax: A generative introduction. John Wiley & Sons.