Might refer to either:
A verb whose direct object is the same as its subject, for example, "I wash myself". This includes reciprocal, autocausative, anticausative, intransitive, impersonal, or inherent verb forms and conjugations. (details on the wiki link above)
A noun phrase that obligatorily gets its meaning from another noun phrase in the sentence.
Singular: myself, yourself, himself, herself, itself
Plural: ourselves, yourselves, themselves