Mononucleosis is usually caused by this virus, EBV for short
It typically occurs in... [DOC] [TLE] Mononucleosis, Infectious - catch, body, viral, What Is Infectious ... [PAR] Mononucleosis, or "mono" for short, is often called the "kissing disease," and ... 
they are referring to the infection caused by the Epstein-Barr virus (EBV).