Raymond de Saussure introduced the term in 1920 by way of analogy to its logical converse in psychoanalysis, the Oedipus complex, and it may be used to cover different degrees of attachment, including domineering but asexual mother love – something perhaps particularly prevalent with an intelligent son and an absent/weak father figure.
The Jocasta complex is named for Jocasta, the fictional Greek queen who had a sexual relationship with her son. The Jocasta complex is similar to the Oedipus complex, in which a son has sexual desire towards his mother. The term is a bit of an extrapolation, since in the original story Oedipus was unaware Jocasta was his mother and married her. The usage in modern contexts involves a son with full knowledge of who his mother is.
Theodor Reik saw the 'Jocasta mother', with an unfulfilled adult relationship of their own and over-concern for their child instead, as a prime source of neurosis.
George Devereux went further, arguing that the child's oedipal complex was itself triggered by a pre-existing parental complex (Jocasta/Laius).
Eric Berne also explored the other (parental) side of the oedipus complex, pointing to related family dramas such as “mother sleeping with daughter's boyfriend...when mother has no son to play Jocasta with”.