Immune complex - also called 'Antibody-Antigen complex', complex which results from the binding of antibody to the antigen. It can also be accompanied by the binding of the complement (C3b). The size of the complex may vary depending on the number of the level of antigens and antibodies in the organism. In excess of antigen, the complexes formed are small and readily soluble, however in case of antibody excess, the complexes tend to be much larger.
Reference: Murphy, Kenneth P., Janeway's immunobiology, 2011, page 414-416, 452