In psychology and medicine, a syndrome is when there are multiple symptoms. These symptoms may be related. In some cases the way in which they are related is known, in other cases it isn't. When both the relationship of symptoms and their causes are known, people generally talk about a disease.
Symptoms that occur together in similar contexts are often related, or have a common cause. Some syndromes, such as Down syndrome have only one cause. In the case of Down syndrome, the cause is known. Other syndromes, such as Pakinsonian syndrome may have many causes, and finding the exact cause may be difficult.