Some sources use the terms "ideas of reference" and "delusions of reference" interchangeably. Other sources differentiate between the two, saying that ideas of reference have less impact on the person's life as a whole. According to these sources, if ideas of reference reach the point of strongly held beliefs or cause impairment of functioning, they become delusions of reference.
Sources:
Medical Definition of Ideas of Reference
Delusions of Reference Versus Ideas of Reference
Idea of Reference

