workplace affair; office adultery
Refers specifically to an extramarital romantic or sexual relationship between colleagues within the same company or workplace.
Their workplace affair was discovered, and both of them quit the company.
Office adultery often creates an awkward atmosphere among colleagues.
不倫 is a general term for adultery or an extramarital affair, while 社内不倫 specifies that the affair takes place within a workplace setting.
Compound of 社内 (within the company) and 不倫 (adultery, immorality). The exact origin is uncertain, but it is a modern term reflecting social awareness of workplace relationships.