An Integrated Shield Plan combines MediShield Life with extra cover from a private insurer, such as for Class A wards or private hospitals. Singapore Citizens and Permanent Residents buy them for themselves, and part of the premium can be paid from MediSave.
An IP belongs to the employee and stays with them when they change jobs. Group cover belongs to the company and ends when the employee leaves.
Many employees have both. Group cover can pay for costs an IP would leave to the employee, and it gives cover to foreign employees who cannot buy an IP.