Schizoid personality disorder refers to a syndrome marked by a chronic lack of interest in and avoidance of interpersonal relationships as well as emotional coldness in interactions with others; a Cluster A personality disorder characterized by social withdrawal and/or odd or strange mannerisms; symptoms include magical thinking, ideas of reference, illusions, and derealization.

Other /More definition:
schizoid personality disorder refers to Cluster A (odd or eccentric) personality disorder featuring a pervasive pattern of detachment from social relationships and a restricted range of expression of emotions.