Question

what's the difference between a disease and a syndrome?

Answer 1

A syndrome is a set of symptoms or conditions that occur together and suggest the presence of a certain disease or an increased chance of developing the disease.

A disease is the actual diagnosed impairment of health or a condition of abnormal functioning.

Answer 2

Sometimes a syndrome is a disease, sometimes not.
A disease is an alteration from normal physiology that produces distress, impairment, or disability; that has a predictable etiology, course, and often standard set of treatments. A Syndrome is a set of symptoms that often goes together. Often a syndrome can be due to number of different etiologies (causes). For instance, a viral syndrome (like the flu) can be due a number of different viruses (e.g. corona virus, influenza, etc). So sometimes a syndrome is a disease but with various possible exact causes. Other times, a syndrome is a set of symptoms and findings that do not have a known etiology. For instance, many of the psychiatric disorders are completely "syndromic" in that they are a collection of symptoms and findings that go together in a fairly predictable manner, but we know very little about the causes.