From the wonderful Wikipedia:
Early in Jung’s career he coined the term and described the concept of the ‘complex’. Jung claims to have discovered the concept during his word association and galvanic skin response experiments. Freud obviously took up this concept in his Oedipus complex amongst others. Jung seemed to see complexes as quite autonomous parts of psychological life. It is almost as if Jung were describing separate personalities within what is considered a single individual. But to equate Jung’s use of complexes with something along the lines of ‘multiple personality disorder’ would be to stretch the point beyond breaking.