To define engagement briefly, it is taking an active role in the decision-making of your health care and the health care of your loved ones. In this manner, patients and clients are no longer receiving health services passively.
In 2001, The National Academy of Medicine, formerly known as the Institute of Medicine, put together 10 rules pertaining to the rights of the patient and their role in a new medical model called "patient-centered care". In particular, rule 3 states that patients are the source of control whereas previously it was health professionals who controlled care.
This is important because with engagement, the flow of information between health professional and patient are now fluid and transparent. Knowledge is no longer hidden and it invites open discussion about all the options that are available to the patient. This includes exploring benefits and risks of various options and helping the patient choose the best choice of treatment that better suits their needs. The health professional does not dictate what the patient should do but guides them instead.
When guiding a patient through a health decision, the health care provider is understanding of the patient's unique circumstance that brought them to that decision so much so, that in order to ensure that the particular needs of the patient are met, the health professional must act as an advocate as well.